Semiconductor device and structure

ABSTRACT

A semiconductor device including a first layer including first transistors, wherein first logic circuits are constructed by the first transistors, and wherein the first logic circuits include at least one of Inverter, NAND gate, or NOR gate; and a second layer overlaying said first layer, the second layer including second transistors, wherein second logic circuits are constructed by the second transistors; wherein each logic circuit in the first logic circuits has inputs and at least one first output, the inputs are connected to the second logic circuits; wherein each logic circuit in the second logic circuits has a second output, and wherein the first transistors include first selectors adapted to selectively replace at least one of the at least one first outputs with at least one of the second outputs.

CROSS-REFERENCE OF RELATED APPLICATION

This application claims priority of co-pending U.S. patent applicationSer. Nos. 12/423,214, 12/577,532, 12/706,520, 12/792,673, 12/847,911,12/859,665, 12/900,379, 12/949,617, and 12/970,602 the contents of whichare incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the general field of Integrated Circuit(IC) devices and fabrication methods, and more particularly tomultilayer or Three Dimensional Integrated Circuit (3D IC) devices andfabrication methods.

2. Discussion of Background Art

Semiconductor manufacturing is known to improve device density in anexponential manner over time, but such improvements come with a price.The mask set cost required for each new process technology has also beenincreasing exponentially. While 20 years ago a mask set cost less than$20,000, it is now quite common to be charged more than $1M for today'sstate of the art device mask set.

These changes represent an increasing challenge primarily to customproducts, which tend to target smaller volume and less diverse marketstherefore making the increased cost of product development very hard toaccommodate.

Custom Integrated Circuits can be segmented into two groups. The firstgroup includes devices that have all their layers custom made. Thesecond group includes devices that have at least some generic layersused across different custom products. Well-known examples of the secondkind are Gate Arrays, which use generic layers for all layers up to acontact layer that couples the silicon devices to the metal conductors,and Field Programmable Gate Array (FPGA) devices where all the layersare generic. The generic layers in such devices are mostly a repeatingpattern structure, called a Master Slice, in an array form.

The logic array technology is based on a generic fabric that iscustomized for a specific design during the customization stage. For anFPGA the customization is done through programming by electricalsignals. For Gate Arrays, which in their modern form are sometimescalled Structured Application Specific Integrated Circuits (orStructured ASICs), the customization is by at least one custom layer,which might be done with Direct Write eBeam or with a custom mask. Asdesigns tend to be highly variable in the amount of logic and memory andtype of input & output (I/O) each one needs, vendors of logic arrayscreate product families, each product having a different number ofMaster Slices covering a range of logic, memory size and I/O options.Yet, it is always a challenge to come up with minimum set of MasterSlices that will provide a good fit for the maximal number of designsbecause it is quite costly if a dedicated mask set is required for eachproduct.

U.S. Pat. No. 4,733,288 issued to Sato in March 1988 (“Sato”), disclosesa method “to provide a gate-array LSI chip which can be cut into aplurality of chips, each of the chips having a desired size and adesired number of gates in accordance with a circuit design.” Thereferences cited in Sato present a few alternative methods to utilize ageneric structure for different sizes of custom devices.

The array structure fits the objective of variable sizing. Thedifficulty to provide variable-sized array structure devices is due tothe need of providing I/O cells and associated pads to connect thedevice to the package. To overcome this limitation Sato suggests amethod where I/O could be constructed from the transistors that are alsoused for the general logic gates. Anderson also suggested a similarapproach. U.S. Pat. No. 5,217,916 issued to Anderson et al. on Jun. 8,1993, discloses a borderless configurable gate array free of predefinedboundaries using transistor gate cells, of the same type of cells usedfor logic, to serve the input and output function. Accordingly, theinput and output functions may be placed to surround the logic arraysized for the specific application. This method places a severelimitation on the I/O cell to use the same type of transistors as usedfor the logic and; hence, would not allow the use of higher operatingvoltages for the I/O.

U.S. Pat. No. 7,105,871 issued to Or-Bach et al. on Sep. 12, 2006,discloses a semiconductor device that includes a borderless logic arrayand area I/Os. The logic array may comprise a repeating core, and atleast one of the area I/Os may be a configurable I/O.

In the past it was reasonable to design an I/O cell that could beconfigured to the various needs of most customers. The ever increasingneed of higher data transfer rate in and out of the device drove thedevelopment of special serial I/O circuits called SerDes(Serializer/Deserializer) transceivers. These circuits are complex andrequire a far larger silicon area than conventional I/Os. Consequently,the variations needed are combinations of various amounts of logic,various amounts and types of memories, and various amounts and types ofI/O. This implies that even the use of the borderless logic array of theprior art will still require multiple expensive mask sets.

The most common FPGAs in the market today are based on Static RandomAccess Memory (SRAM) as the programming element. Floating-Gate Flashprogrammable elements are also utilized to some extent. Less commonly,FPGAs use an antifuse as the programming element. The first generationof antifuse FPGAs used antifuses that were built directly in contactwith the silicon substrate itself. The second generation moved theantifuse to the metal layers to utilize what is called the Metal toMetal Antifuse. These antifuses function like programmable vias.However, unlike vias that are made with the same metal that is used forthe interconnection, these antifuses generally use amorphous silicon andsome additional interface layers. While in theory antifuse technologycould support a higher density than SRAM, the SRAM FPGAs are dominatingthe market today. In fact, it seems that no one is advancing AntifuseFPGA devices anymore. One of the severe disadvantages of antifusetechnology has been their lack of re-programmability. Anotherdisadvantage has been the special silicon manufacturing process requiredfor the antifuse technology which results in extra development costs andthe associated time lag with respect to baseline IC technology scaling.

The general disadvantage of common FPGA technologies is their relativelypoor use of silicon area. While the end customer only cares to have thedevice perform his desired function, the need to program the FPGA to anyfunction requires the use of a very significant portion of the siliconarea for the programming and programming check functions.

Some embodiments of the present invention seek to overcome the prior-artlimitations and provide some additional benefits by making use ofspecial types of transistors that are fabricated above or below theantifuse configurable interconnect circuits and thereby allow far betteruse of the silicon area.

One type of such transistors is commonly known in the art as Thin FilmTransistors or TFT. Thin Film Transistors has been proposed and used forover three decades. One of the better-known usages has been for displayswhere the TFT are fabricated on top of the glass used for the display.Other type of transistors that could be fabricated above the antifuseconfigurable interconnect circuits are called Vacuum Field EffectTransistor (FET) and was introduced three decades ago such as in U.S.Pat. No. 4,721,885.

Other techniques could also be used such as employing Silicon OnInsulator (SOI) technology. In U.S. Pat. Nos. 6,355,501 and 6,821,826,both assigned to IBM, a multilayer three-dimensional ComplementaryMetal-Oxide-Semiconductor (CMOS) Integrated Circuit is proposed. Itsuggests bonding an additional thin SOI wafer on top of another SOIwafer forming an integrated circuit on top of another integrated circuitand connecting them by the use of a through-silicon-via, or thru layervia (TLV). Substrate supplier Soitec SA, of Bernin, France is nowoffering a technology for stacking of a thin layer of a processed waferon top of a base wafer.

Integrating top layer transistors above an insulation layer is notcommon in an IC because the quality and density of prior art top layertransistors are inferior to those formed in the base (or substrate)layer. The substrate may be formed of mono-crystalline silicon and maybe ideal for producing high density and high quality transistors, andhence preferable. There are some applications where it has beensuggested to build memory bit cells using such transistors as in U.S.Pat. Nos. 6,815,781, 7,446,563 and a portion of an SRAM based FPGA suchas in U.S. Pat. Nos. 6,515,511 and 7,265,421.

Embodiments of the present invention seek to take advantage of the toplayer transistor to provide a much higher density antifuse-basedprogrammable logic. An additional advantage for such use will be theoption to further reduce cost in high volume production by utilizingcustom mask(s) to replace the antifuse function, thereby eliminating thetop layer(s) anti-fuse programming logic altogether.

Additionally some embodiments of the present invention may provideinnovative alternatives for multi-layer 3D IC technology. As on-chipinterconnects are becoming the limiting factor for performance and powerenhancement with device scaling, 3D IC may be an important technologyfor future generations of ICs. Currently the only viable technology for3D IC is to finish the IC by the use of Through-Silicon-Via (TSV). Theproblem with TSVs is that they are relatively large (a few microns eachin area) and therefore may lead to highly limited vertical connectivity.The present invention may provide multiple alternatives for 3D IC withan order of magnitude improvement in vertical connectivity.

Constructing future 3D ICs will require new architectures and new waysof thinking. In particular, yield and reliability of extremely complexthree dimensional systems will have to be addressed, particularly giventhe yield and reliability difficulties encountered in building complexApplication Specific Integrated Circuits (ASIC) of recent deep submicronprocess generations.

Fortunately, current testing techniques will likely prove applicable to3D IC manufacturing, though they will be applied in very different ways.FIG. 116 illustrates a prior art set scan architecture in a 2D IC ASIC11600. The ASIC functionality is present in logic clouds 11620, 11622,11624 and 11626 which are interspersed with sequential cells like, forexample, pluralities of flip-flops indicated at 11612, 11614 and 11616.The ASIC 11600 also has input pads 11630 and output pads 11640. Theflip-flops are typically provided with circuitry to allow them tofunction as a shift register in a test mode. In FIG. 116 the flip-flopsform a scan register chain where pluralities of flip-flops 11612, 11614and 11616 are coupled together in series with Scan Test Controller11610. One scan chain is shown in FIG. 116, but in a practical designcomprising millions of flip-flops, many sub-chains will be used.

In the test architecture of FIG. 116, test vectors are shifted into thescan chain in a test mode. Then the part is placed into operating modefor one or more clock cycles, after which the contents of the flip-flopsare shifted out and compared with the expected results. This may providean excellent way to isolate errors and diagnose problems, though thenumber of test vectors in a practical design can be very large and anexternal tester may be utilized.

FIG. 117 shows a prior art boundary scan architecture in exemplary ASIC11700. The part functionality is shown in logic function block 11710.The part also has a variety of input/output cells 11720, each comprisinga bond pad 11722, an input buffer 11724, and a tri-state output buffer11726. Boundary Scan Register Chains 11732 and 11734 are shown coupledin series with Scan Test Control block 11730. This architecture operatesin a similar manner as the set scan architecture of FIG. 116. Testvectors are shifted in, the part is clocked, and the results are thenshifted out to compare with expected results. Typically, set scan andboundary scan are used together in the same ASIC to provide completetest coverage.

FIG. 118 shows a prior art Built-In Self Test (BIST) architecture fortesting a logic block 11800 which comprises a core block function 11810(what is being tested), inputs 11812, outputs 11814, a BIST Controller11820, an input Linear Feedback Shift Register (LFSR) 11822, and anoutput Cyclical Redundancy Check (CRC) circuit 11824. Under control ofBIST Controller 11820, LFSR 11822 and CRC 11824 are seeded (i.e., set toa known starting value), the block 11800 is clocked a predeterminednumber of times with LFSR 11822 presenting pseudo-random test vectors tothe inputs of Block Function 11810 and CRC 11824 monitoring the outputsof Block Function 11810. After the predetermined number of clocks, thecontents of CRC 11824 are compared to the expected value (or signature).If the signature matches, block 11800 passes the test and is deemedgood. This sort of testing is good for fast “go” or “no go” testing asit is self-contained to the block being tested and does not requirestoring a large number of test vectors or use of an external tester.BIST, set scan, and boundary scan techniques are often combined incomplementary ways on the same ASIC. A detailed discussion of the theoryof LSFRs and CRCs can be found in Digital Systems Testing and TestableDesign, by Abramovici, Breuer and Friedman, Computer Science Press,1990, pp 432-447.

Another prior art technique that is applicable to the yield andreliability of 3D ICs is Triple Modular Redundancy. This is a techniquewhere the circuitry is instantiated in a design in triplicate and theresults are compared. Because two or three of the circuit outputs arealways in agreement (as is the case with binary signals) votingcircuitry (or majority-of-three or MAJ3) takes that as the result. Whileprimarily a technique used for noise suppression in high reliability orradiation tolerant systems in military, aerospace and spaceapplications, it also can be used as a way of masking errors in faultycircuits since if any two of three replicated circuits are functionalthe system will behave as if it is fully functional. A discussion of theradiation tolerant aspects of TMR systems, Single Event Effects (SEE),Single Event Upsets (SEU) and Single Event Transients (SET) can be foundin U.S. Patent Application Publication 2009/0204933 to Rezgui(“Rezgui”).

Additionally the 3D technology according to some embodiments of thepresent invention may enable some very innovative IC alternatives withreduced development costs, increased yield, and other importantbenefits.

SUMMARY

Embodiments of the present invention seek to provide a new method forsemiconductor device fabrication that may be highly desirable for customproducts. Embodiments of the present invention suggest the use of are-programmable antifuse in conjunction with ‘Through Silicon Via’ toconstruct a new type of configurable logic, or as usually called, FPGAdevices. Embodiments of the present invention may provide a solution tothe challenge of high mask-set cost and low flexibility that exists inthe current common methods of semiconductor fabrication. An additionaladvantage of some embodiments of the present invention is that it couldreduce the high cost of manufacturing the many different mask setsneeded in order to provide a commercially viable logic family with arange of products each with a different set of master slices.Embodiments of the present invention may improve upon the prior art inmany respects, which may include the way the semiconductor device isstructured and methods related to the fabrication of semiconductordevices.

Embodiments of the present invention reflect the motivation to save onthe cost of masks with respect to the investment that would otherwisehave been necessary to put in place a commercially viable set of masterslices. Embodiments of the present invention also seek to provide theability to incorporate various types of memory blocks in theconfigurable device. Embodiments of the present invention provide amethod to construct a configurable device with the desired amount oflogic, memory, I/Os, and analog functions.

In addition, embodiments of the present invention allow the use ofrepeating logic tiles that provide a continuous terrain of logic.Embodiments of the present invention show that with Through-Silicon-Via(TSV) a modular approach could be used to construct various configurablesystems. Once a standard size and location of TSV has been defined onecould build various configurable logic dies, configurable memory dies,configurable I/O dies and configurable analog dies which could beconnected together to construct various configurable systems. In fact itmay allow mix and match between configurable dies, fixed function dies,and dies manufactured in different processes.

Embodiments of the present invention seek to provide additional benefitsby making use of special type of transistors that are placed above orbelow the antifuse configurable interconnect circuits and thereby allowa far better use of the silicon area. In general an FPGA device thatutilizes antifuses to configure the device function may include theelectronic circuits to program the antifuses. The programming circuitsmay be used primarily to configure the device and are mostly an overheadonce the device is configured. The programming voltage used to programthe antifuse may typically be significantly higher than the voltage usedfor the operating circuits of the device. The design of the antifusestructure may be designed such that an unused antifuse will notaccidentally get fused. Accordingly, the incorporation of the antifuseprogramming in the silicon substrate may need special attention for thishigher voltage, and additional silicon area may, accordingly, beallocated.

Unlike the operating transistors that are desired to operate as fast aspossible, to enable fast system performance, the programming circuitscould operate relatively slowly. Accordingly using a thin filmtransistor for the programming circuits could fit very well with thefunction and would reduce the needed silicon area.

The programming circuits may, therefore, be constructed with thin filmtransistors, which may be fabricated after the fabrication of theoperating circuitry, on top of the configurable interconnection layersthat incorporate and use the antifuses. An additional advantage of suchembodiments of the present invention is the ability to reduce cost ofthe high volume production. One may only need to use mask-defined linksinstead of the antifuses and their programming circuits. One custom viamask may be used, and this may save steps associated with thefabrication of the antifuse layers, the thin film transistors, and/orthe associated connection layers of the programming circuitry.

In accordance with an embodiment of the present invention an IntegratedCircuit device is thus provided, comprising; a plurality of antifuseconfigurable interconnect circuits and plurality of transistors toconfigure at least one of said antifuses; wherein said transistors arefabricated after said antifuse.

Further provided in accordance with an embodiment of the presentinvention is an Integrated Circuit device comprising; a plurality ofantifuse configurable interconnect circuits and plurality of transistorsto configure at least one of said antifuses; wherein said transistorsare placed over said antifuse.

Still further in accordance with an embodiment of the present inventionthe Integrated Circuit device comprises second antifuse configurablelogic cells and plurality of second transistors to configure said secondantifuses wherein these second transistors are fabricated before saidsecond antifuses.

Still further in accordance with an embodiment of the present inventionthe Integrated Circuit device comprises also second antifuseconfigurable logic cells and a plurality of second transistors toconfigure said second antifuses wherein said second transistors areplaced underneath said second antifuses.

Further provided in accordance with an embodiment of the presentinvention is an Integrated Circuit device comprising; first antifuselayer, at least two metal layers over it and a second antifuse layeroverlaying the two metal layers.

In accordance with an embodiment of the present invention a configurablelogic device is presented, comprising: antifuse configurable look uptable logic interconnected by antifuse configurable interconnect.

In accordance with an embodiment of the present invention a configurablelogic device is also provided, comprising: plurality of configurablelook up table logic, plurality of configurable programmable logic array(PLA) logic, and plurality of antifuse configurable interconnect.

In accordance with an embodiment of the present invention a configurablelogic device is also provided, comprising: plurality of configurablelook up table logic and plurality of configurable drive cells whereinthe drive cells are configured by plurality of antifuses.

In accordance with an embodiment of the present invention a configurablelogic device is additionally provided, comprising: configurable logiccells interconnected by a plurality of antifuse configurableinterconnect circuits wherein at least one of the antifuse configurableinterconnect circuits is configured as part of a non volatile memory.

Further in accordance with an embodiment of the present invention theconfigurable logic device comprises at least one antifuse configurableinterconnect circuit, which is also configurable to a PLA function.

In accordance with an alternative embodiment of the present invention anintegrated circuit system is also provided, comprising a configurablelogic die and an I/O die wherein the configurable logic die is connectedto the I/O die by the use of Through-Silicon-Via.

Further in accordance with an embodiment of the present invention theintegrated circuit system comprises; a configurable logic die and amemory die wherein these dies are connected by the use ofThrough-Silicon-Via.

Still further in accordance with an embodiment of the present inventionthe integrated circuit system comprises a first configurable logic dieand second configurable logic die wherein the first configurable logicdie and the second configurable logic die are connected by the use ofThrough-Silicon-Via.

Moreover in accordance with an embodiment of the present invention theintegrated circuit system comprises an I/O die that was fabricatedutilizing a different process than the process utilized to fabricate theconfigurable logic die.

Further in accordance with an embodiment of the present invention theintegrated circuit system comprises at least two logic dies connected bythe use of Through-Silicon-Via and wherein some of theThrough-Silicon-Vias are utilized to carry the system bus signal.

Moreover in accordance with an embodiment of the present invention theintegrated circuit system comprises at least one configurable logicdevice.

Further in accordance with an embodiment of the present invention theintegrated circuit system comprises, an antifuse configurable logic dieand programmer die and these dies are connected by the use ofThrough-Silicon-Via.

Additionally there is a growing need to reduce the impact of inter-chipinterconnects. In fact, interconnects are now dominating IC performanceand power. One solution to shorten interconnect may be to use a 3D IC.Currently, the only known way for general logic 3D IC is to integratefinished device one on top of the other by utilizingThrough-Silicon-Vias as now called TSVs. The problem with TSVs is thattheir large size, usually a few microns each, may severely limit thenumber of connections that can be made. Some embodiments of the presentinvention may provide multiple alternatives to constructing a 3D ICwherein many connections may be made less than one micron in size, thusenabling the use of 3D IC technology for most device applications.

Additionally some embodiments of this invention may offer new devicealternatives by utilizing the proposed 3D IC technology.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will be understood andappreciated more fully from the following detailed description, taken inconjunction with the drawings in which:

FIG. 1 is a circuit diagram illustration of a prior art;

FIG. 2 is a cross-section illustration of a portion of a prior artrepresented by the circuit diagram of FIG. 1;

FIG. 3A is a drawing illustration of a programmable interconnectstructure;

FIG. 3B is a drawing illustration of a programmable interconnectstructure;

FIG. 4A is a drawing illustration of a programmable interconnect tile;

FIG. 4B is a drawing illustration of a programmable interconnect of 2×2tiles;

FIG. 5A is a drawing illustration of an inverter logic cell;

FIG. 5B is a drawing illustration of a buffer logic cell;

FIG. 5C is a drawing illustration of a configurable strength bufferlogic cell;

FIG. 5D is a drawing illustration of a D-Flip Flop logic cell;

FIG. 6 is a drawing illustration of a LUT 4 logic cell;

FIG. 6A is a drawing illustration of a PLA logic cell;

FIG. 7 is a drawing illustration of a programmable cell;

FIG. 8 is a drawing illustration of a programmable device layersstructure;

FIG. 8A is a drawing illustration of a programmable device layersstructure;

FIG. 8B-8I are drawing illustrations of the preprocessed wafers andlayers and generalized layer transfer;

FIG. 9A through 9C are a drawing illustration of an IC system utilizingThrough Silicon Via of a prior art;

FIG. 10A is a drawing illustration of continuous array wafer of a priorart;

FIG. 10B is a drawing illustration of continuous array portion of waferof a prior art;

FIG. 10C is a drawing illustration of continuous array portion of waferof a prior art;

FIG. 11A through 11F are a drawing illustration of one reticle site on awafer;

FIG. 12A through 12E are a drawing illustration of Configurable system;and

FIG. 13 a drawing illustration of a flow chart for 3D logicpartitioning;

FIG. 14 is a drawing illustration of a layer transfer process flow;

FIG. 15 is a drawing illustration of an underlying programming circuits;

FIG. 16 is a drawing illustration of an underlying isolation transistorscircuits;

FIG. 17A is a topology drawing illustration of underlying back biascircuitry;

FIG. 17B is a drawing illustration of underlying back bias circuits;

FIG. 17C is a drawing illustration of power control circuits

FIG. 17D is a drawing illustration of probe circuits

FIG. 18 is a drawing illustration of an underlying SRAM;

FIG. 19A is a drawing illustration of an underlying I/O;

FIG. 19B is a drawing illustration of side “cut”;

FIG. 19C is a drawing illustration of a 3D IC system;

FIG. 19D is a drawing illustration of a 3D IC processor and DRAM system;

FIG. 19E is a drawing illustration of a 3D IC processor and DRAM system;

FIG. 19F is a drawing illustration of a custom SOI wafer used to buildthrough-silicon connections;

FIG. 19G is a drawing illustration of a prior art method to makethrough-silicon vias;

FIG. 19H is a drawing illustration of a process flow for making customSOI wafers;

FIG. 19I is a drawing illustration of a processor-DRAM stack;

FIG. 19J is a drawing illustration of a process flow for making customSOI wafers;

FIG. 20 is a drawing illustration of a layer transfer process flow;

FIG. 21A is a drawing illustration of a pre-processed wafer used for alayer transfer;

FIG. 21B is a drawing illustration of a pre-processed wafer ready for alayer transfer;

FIG. 22A-22H are drawing illustrations of formation of top planartransistors;

FIG. 23A, 23B is a drawing illustration of a pre-processed wafer usedfor a layer transfer;

FIG. 24A-24F are drawing illustrations of formation of top planartransistors;

FIG. 25A, 25B is a drawing illustration of a pre-processed wafer usedfor a layer transfer;

FIG. 26A-26E are drawing illustrations of formation of top planartransistors;

FIG. 27A, 27B is a drawing illustration of a pre-processed wafer usedfor a layer transfer;

FIG. 28A-28E are drawing illustrations of formations of top transistors;

FIG. 29A-29G are drawing illustrations of formations of top planartransistors;

FIG. 30 is a drawing illustration of a donor wafer;

FIG. 31 is a drawing illustration of a transferred layer on top of amain wafer;

FIG. 32 is a drawing illustration of a measured alignment offset;

FIG. 33A, 33B is a drawing illustration of a connection strip;

FIG. 34A-34E are drawing illustrations of pre-processed wafers used fora layer transfer;

FIG. 35A-35G are drawing illustrations of formations of top planartransistors;

FIG. 36 is a drawing illustration of a tile array wafer;

FIG. 37 is a drawing illustration of a programmable end device;

FIG. 38 is a drawing illustration of modified JTAG connections;

FIG. 39A-39C are drawing illustration of pre-processed wafers used forvertical transistors;

FIG. 40A-40I are drawing illustrations of a vertical n-MOSFET toptransistor;

FIG. 41 is a drawing illustration of a 3D IC system with redundancy;

FIG. 42 is a drawing illustration of an inverter cell;

FIG. 43 A-C is a drawing illustration of preparation steps for formationof a 3D cell;

FIG. 44 A-F is a drawing illustration of steps for formation of a 3Dcell;

FIG. 45 A-G is a drawing illustration of steps for formation of a 3Dcell;

FIG. 46 A-C is a drawing illustration of a layout and cross sections ofa 3D inverter cell;

FIG. 47 is a drawing illustration of a 2-input NOR cell;

FIG. 48 A-C are drawing illustrations of a layout and cross sections ofa 3D 2-input NOR cell;

FIG. 49 A-C are drawing illustrations of a 3D 2-input NOR cell;

FIG. 50 A-D are drawing illustrations of a 3D CMOS Transmission cell;

FIG. 51A-D are drawing illustrations of a 3D CMOS SRAM cell;

FIG. 52A, 52B are device simulations of a junction-less transistor;

FIG. 53 A-E are drawing illustrations of a 3D CAM cell;

FIG. 54 A-C are drawing illustrations of the formation of ajunction-less transistor;

FIG. 55 A-I are drawing illustrations of the formation of ajunction-less transistor;

FIG. 56A-M are drawing illustrations of the formation of a junction-lesstransistor;

FIG. 57A-G are drawing illustrations of the formation of a junction-lesstransistor;

FIG. 58 A-G are drawing illustrations of the formation of ajunction-less transistor;

FIG. 59 is a drawing illustration of a metal interconnect stack priorart;

FIG. 60 is a drawing illustration of a metal interconnect stack;

FIG. 61 A-I are drawing illustrations of a junction-less transistor;

FIG. 62 A-D are drawing illustrations of a 3D NAND2 cell;

FIG. 63 A-G are drawing illustrations of a 3D NAND8 cell;

FIG. 64 A-G are drawing illustrations of a 3D NOR8 cell;

FIG. 65A-C are drawing illustrations of the formation of a junction-lesstransistor;

FIG. 66 are drawing illustrations of recessed channel array transistors;

FIG. 67A-F are drawing illustrations of formation of recessed channelarray transistors;

FIG. 68A-F are drawing illustrations of formation of spherical recessedchannel array transistors;

FIG. 69 is a drawing illustration of a donor wafer;

FIGS. 70 A, B, B-1, and C-H are drawing illustrations of formation oftop planar transistors;

FIG. 71 is a drawing illustration of a layout for a donor wafer;

FIG. 72 A-F are drawing illustrations of formation of top planartransistors;

FIG. 73 is a drawing illustration of a donor wafer;

FIG. 74 is a drawing illustration of a measured alignment offset;

FIG. 75 is a drawing illustration of a connection strip;

FIG. 76 is a drawing illustration of a layout for a donor wafer;

FIG. 77 is a drawing illustration of a connection strip;

FIG. 78A, 78B, 78C are drawing illustrations of a layout for a donorwafer;

FIG. 79 is a drawing illustration of a connection strip;

FIG. 80 is a drawing illustration of a connection strip array structure;

FIG. 81 A-F are drawing illustrations of a formation of top planartransistors;

FIG. 82 A-G are drawing illustrations of a formation of top planartransistors;

FIG. 83 A-L are drawing illustrations of a formation of top planartransistors;

FIG. 83 L1-L4 are drawing illustrations of a formation of top planartransistors;

FIG. 84 A-G are drawing illustrations of continuous transistor arrays;

FIG. 85 A-E are drawing illustrations of formation of top planartransistors;

FIG. 86A is a drawing illustration of a 3D logic IC structured forrepair;

FIG. 86B is a drawing illustration of a 3D IC with scan chain confinedto each layer;

FIG. 86C is a drawing illustration of contact-less testing;

FIG. 87 is a drawing illustration of a Flip Flop designed for repairable3D IC logic;

FIG. 88 A-F are drawing illustrations of a formation of 3D DRAM;

FIG. 89 A-D are drawing illustrations of a formation of 3D DRAM;

FIG. 90 A-F are drawing illustrations of a formation of 3D DRAM;

FIG. 91 A-L are drawing illustrations of a formation of 3D DRAM;

FIG. 92A-F are drawing illustrations of a formation of 3D DRAM;

FIG. 93 A-D are drawing illustrations of an advanced TSV flow;

FIG. 94 A-C are drawing illustrations of an advanced TSVmulti-connections flow;

FIG. 95A-J are drawing illustrations of formation of CMOS recessedchannel array transistors;

FIG. 96A-J are drawing illustrations of the formation of a junction-lesstransistor;

FIG. 97 is a drawing illustration of the basics of floating body DRAM;

FIG. 98A-H are drawing illustrations of the formation of a floating bodyDRAM transistor;

FIG. 99A-M are drawing illustrations of the formation of a floating bodyDRAM transistor;

FIG. 100A-L are drawing illustrations of the formation of a floatingbody DRAM transistor;

FIG. 101A-K are drawing illustrations of the formation of a resistivememory transistor;

FIG. 102A-L are drawing illustrations of the formation of a resistivememory transistor;

FIG. 103A-M are drawing illustrations of the formation of a resistivememory transistor;

FIG. 104A-F are drawing illustrations of the formation of a resistivememory transistor;

FIG. 105A-G are drawing illustrations of the formation of a charge trapmemory transistor;

FIG. 106A-G are drawing illustrations of the formation of a charge trapmemory transistor;

FIG. 107A-G are drawing illustrations of the formation of a floatinggate memory transistor;

FIG. 108A-H are drawing illustrations of the formation of a floatinggate memory transistor;

FIG. 109A-K are drawing illustrations of the formation of a resistivememory transistor;

FIG. 110A-J are drawing illustrations of the formation of a resistivememory transistor with periphery on top;

FIG. 111A-D are exemplary drawing illustrations of a generalized layertransfer process flow with alignment windows;

FIG. 112 is a drawing illustration of a heat spreader in a 3D IC;

FIG. 113A-B are drawing illustrations of an integrated heat removalconfiguration for 3D ICs;

FIG. 114 is a drawing illustration of a field repairable 3D IC;

FIG. 115 is a drawing illustration of a Triple Modular Redundancy 3D IC;

FIG. 116 is a drawing illustration of a set scan architecture of theprior art;

FIG. 117 is a drawing illustration of a boundary scan architecture ofthe prior art;

FIG. 118 is a drawing illustration of a BIST architecture of the priorart;

FIG. 119 is a drawing illustration of a second field repairable 3D IC;

FIG. 120 is a drawing illustration of a scan flip-flop suitable for usewith the 3D IC of FIG. 119;

FIG. 121A is a drawing illustration of a third field repairable 3D IC;

FIG. 121B is a drawing illustration of additional aspects of the fieldrepairable 3D IC of FIG. 121A;

FIG. 122 is a drawing illustration of a fourth field repairable 3D IC;

FIG. 123 is a drawing illustration of a fifth field repairable 3D IC;

FIG. 124 is a drawing illustration of a sixth field repairable 3D IC;

FIG. 125A is a drawing illustration of a seventh field repairable 3D IC;

FIG. 125B is a drawing illustration of additional aspects of the fieldrepairable 3D IC of FIG. 125A;

FIG. 126 is a drawing illustration of an eighth field repairable 3D IC;

FIG. 127 is a drawing illustration of a second Triple Modular Redundancy3D IC;

FIG. 128 is a drawing illustration of a third Triple Modular Redundancy3D IC;

FIG. 129 is a drawing illustration of a fourth Triple Modular Redundancy3D IC;

FIG. 130A is a drawing illustration of a first via metal overlappattern;

FIG. 130B is a drawing illustration of a second via metal overlappattern;

FIG. 130C is a drawing illustration of the alignment of the via metaloverlap patterns of FIGS. 130A and 130B in a 3D IC;

FIG. 130D is a drawing illustration of a side view of the structure ofFIG. 130C;

FIG. 131A is a drawing illustration of a third via metal overlappattern;

FIG. 131B is a drawing illustration of a fourth via metal overlappattern;

FIG. 131C is a drawing illustration of the alignment of the via metaloverlap patterns of FIGS. 131A and 131B in a 3D IC;

FIG. 132A is a drawing illustration of a fifth via metal overlappattern;

FIG. 132B is a drawing illustration of the alignment of three instancesof the via metal overlap patterns of FIG. 132A in a 3D IC;

FIG. 133A-I are exemplary drawing illustrations of formation of arecessed channel array transistor with source and drain silicide;

FIG. 134A-F are drawing illustrations of a 3D IC FPGA process flow;

FIG. 135A-D are drawing illustrations of an alternative 3D IC FPGAprocess flow;

FIG. 136 is a drawing illustration of an NVM FPGA configuration cell;

FIG. 137A-G are drawing illustrations of a 3D IC NVM FPGA configurationcell process flow;

FIG. 138A-B are drawing illustrations of prior-art packaging schemes;

FIG. 139A-F are drawing illustrations of a process flow to constructpackages;

FIG. 140A-F are drawing illustrations of a process flow to constructpackages;

FIG. 141 is a drawing illustration of a technique to provide a highdensity of connections between different chips on the same packagingsubstrate;

FIG. 142A-C are drawing illustrations of process to reduce surfaceroughness after a cleave;

FIG. 143A-D are drawing illustrations of a prior art process toconstruct shallow trench isolation regions;

FIG. 144A-D are drawing illustrations of a sub-400° C. process toconstruct shallow trench isolation regions;

FIG. 145A-J are drawing illustrations of a process flow formanufacturing junction-less transistors with reduced lithography steps;

FIG. 146A-K are drawing illustrations of a process flow formanufacturing FinFET transistors with reduced lithography steps;

FIG. 147A-G are drawing illustrations of a process flow formanufacturing planar transistors with reduced lithography steps;

FIG. 148A-H are drawing illustrations of a process flow formanufacturing 3D stacked planar transistors with reduced lithographysteps;

FIG. 149 is a drawing illustration of 3D stacked peripheral transistorsconstructed above a memory layer;

FIG. 150A-C are drawing illustrations of a process to transfer thinlayers;

FIG. 151A-F are drawing illustrations of a process flow formanufacturing junction-less recessed channel array transistors;

FIG. 152A-I are drawing illustrations of a process flow formanufacturing trench MOSFETs.

FIG. 153A-D are drawing illustrations of a generalized layer transferprocess flow with alignment windows for stacking sub-stacks; and

FIG. 154A-F are drawing illustrations of a generalized layer transferprocess flow with alignment windows for stacking sub-stacks utilizing acarrier substrate;

DETAILED DESCRIPTION

Embodiments of the present invention are now described with reference tothe drawing figures. Persons of ordinary skill in the art willappreciate that the description and figures illustrate rather than limitthe invention and that in general the figures are not drawn to scale forclarity of presentation. Such skilled persons will also realize thatmany more embodiments are possible by applying the inventive principlescontained herein and that such embodiments fall within the scope of theinvention which is not to be limited except by the appended claims.

FIG. 1 illustrates a circuit diagram illustration of a prior art, where,for example, 860-1 to 860-4 are the programming transistors to programantifuse 850-1,1.

FIG. 2 is a cross-section illustration of a portion of a prior artrepresented by the circuit diagram of FIG. 1 showing the programmingtransistor 860-1 built as part of the silicon substrate.

FIG. 3A is a drawing illustration of a programmable interconnect tile.310-1 is one of 4 horizontal metal strips, which form a band of strips.The typical IC today has many metal layers. In a typical programmabledevice the first two or three metal layers will be used to construct thelogic elements. On top of them metal 4 to metal 7 will be used toconstruct the interconnection of those logic elements. In an FPGA devicethe logic elements are programmable, as well as the interconnectsbetween the logic elements. The configurable interconnect of the presentinvention is constructed from 4 metal layers or more. For example, metal4 and 5 could be used for long strips and metal 6 and 7 would compriseshort strips. Typically the strips forming the programmable interconnecthave mostly the same length and are oriented in the same direction,forming a parallel band of strips as 310-1, 310-2, 310-3 and 310-4.Typically one band will comprise 10 to 40 strips. Typically the stripsof the following layer will be oriented perpendicularly as illustratedin FIG. 3A, wherein strips 310 are of metal 6 and strips 308 are ofmetal 7. In this example the dielectric between metal 6 and metal 7comprises antifuse positions at the crossings between the strips ofmetal 6 and metal 7. Tile 300 comprises 16 such antifuses. 312-1 is theantifuse at the cross of strip 310-4 and 308-4. If activated, it willconnect strip 310-4 with strip 308-4. FIG. 3A was made simplified, asthe typical tile will comprise 10-40 strips in each layer andmultiplicity of such tiles, which comprises the antifuse configurableinterconnect structure.

304 is one of the Y programming transistors connected to strip 310-1.318 is one of the X programming transistors connected to strip 308-4.302 is the Y select logic which at the programming phase allows theselection of a Y programming transistor. 316 is the X select logic whichat the programming phase allows the selection of an X programmingtransistor. Once 304 and 318 are selected the programming voltage 306will be applied to strip 310-1 while strip 308-4 will be groundedcausing the antifuse 312-4 to be activated.

FIG. 3B is a drawing illustration of a programmable interconnectstructure 300B. 300B is variation of 300A wherein some strips in theband are of a different length. Instead of strip 308-4 in this variationthere are two shorter strips 308-4B1 and 308-4B2. This might be usefulfor bringing signals in or out of the programmable interconnectstructure 300B in order to reduce the number of strips in the tile, thatare dedicated to bringing signals in and out of the interconnectstructure versus strips that are available to perform the routing. Insuch variation the programming circuit needs to be augmented to supportthe programming of antifuses 312-3B and 312-4B.

Unlike the prior art, various embodiments of the present inventionsuggest constructing the programming transistors not in the base silicondiffusion layer but rather above or below the antifuse configurableinterconnect circuits. The programming voltage used to program theantifuse is typically significantly higher than the voltage used for theoperational circuits of the device. This is part of the design of theantifuse structure so that the antifuse will not become accidentallyactivated. In addition, extra attention, design effort, and siliconresources might be needed to make sure that the programming phase willnot damage the operating circuits. Accordingly the incorporation of theantifuse programming transistors in the silicon substrate may needattention and extra silicon area.

Unlike the operational transistors that are desired to operate as fastas possible and so to enable fast system performance, the programmingcircuits could operate relatively slowly. Accordingly, a thin filmtransistor for the programming circuits could provide the function andcould reduce the silicon area.

Alternatively other type of transistors, such as Vacuum FET, bipolar,etc., could be used for the programming circuits and may be placed notin the base silicon but rather above or below the antifuse configurableinterconnect.

Yet in another alternative the programming transistors and theprogramming circuits could be fabricated on SOI wafers which may then bebonded to the configurable logic wafer and connected to it by the use ofthrough-silicon-via (TSV), or thru layer via (TLV). An advantage ofusing an SOI wafer for the antifuse programming function is that thehigh voltage transistors that could be built on it are very efficientand could be used for the programming circuit including support functionsuch as the programming controller function. Yet as an additionalvariation, the programming circuits could be fabricated on an olderprocess on SOI wafers to further reduce cost. Or some other processtechnology and/or wafer fab located anywhere in the world.

Also there are advanced technologies to deposit silicon or othersemiconductors layers that could be integrated on top of the antifuseconfigurable interconnect for the construction of the antifuseprogramming circuit. As an example, a recent technology proposed the useof a plasma gun to spray semiconductor grade silicon to formsemiconductor structures including, for example, a p-n junction. Thesprayed silicon may be doped to the respective semiconductor type. Inaddition there are more and more techniques to use graphene and CarbonNano Tubes (CNT) to perform a semiconductor function. For the purpose ofthis present invention we will use the term “Thin-Film-Transistors”asgeneral name for all those technologies, as well as any similartechnologies, known or yet to be discovered.

A common objective is to reduce cost for high volume production withoutredesign and with minimal additional mask cost. The use ofthin-film-transistors, for the programming transistors, enables arelatively simple and direct volume cost reduction. Instead of embeddingantifuses in the isolation layer a custom mask could be used to definevias on substantially all the locations that used to have theirrespective antifuse activated. Accordingly the same connection betweenthe strips that used to be programmed is now connected by fixed vias.This may allow saving the cost associated with the fabrication of theantifuse programming layers and their programming circuits. It should benoted that there might be differences between the antifuse resistanceand the mask defined via resistance. A conventional way to handle it isby providing the simulation models for both options so the designercould validate that the design will work properly in both cases.

An additional objective for having the programming circuits above theantifuse layer is to achieve better circuit density. Many connectionsare needed to connect the programming transistors to their respectivemetal strips. If those connections are going upward they could reducethe circuit overhead by not blocking interconnection routes on theconnection layers underneath.

While FIG. 3A shows an interconnection structure of 4×4 strips, thetypical interconnection structure will have far more strips and in manycases more than 20×30. For a 20×30 tile there is needed about 20+30=50programming transistors. The 20×30 tile area is about 20 hp×30 vp where‘hp’ is the horizontal pitch and ‘vp’ is the vertical pitch. This mayresult in a relatively large area for the programming transistor ofabout 12 hp×vp (20 hp×30 vp/50=12 hp×vp). Additionally, the areaavailable for each connection between the programming layer and theprogrammable interconnection fabric needs to be handled. Accordingly,one or two redistribution layers might be needed in order toredistribute the connection within the available area and then bringthose connections down, preferably aligned so to create minimum blockageas they are routed to the underlying strip 310 of the programmableinterconnection structure.

FIG. 4A is a drawing illustration, of a programmable interconnect tile300 and another programmable interface tile 320. As a higher silicondensity is achieved it becomes desirable to construct the configurableinterconnect in the most compact fashion. FIG. 4B is a drawingillustration of a programmable interconnect of 2×2 tiles. It comprisescheckerboard style of tiles 300 and tiles 320 which is a tile 300rotated by 90 degrees. For a signal to travel South to North, south tonorth strips need to be connected with antifuses such as 406. 406 and410 are antifuses that are positioned at the end of a strip to allow itto connect to another strip in the same direction. The signal travelingfrom South to North is alternating from metal 6 to metal 7. Once thedirection needs to change, an antifuse such as 312-1 is used.

The configurable interconnection structure function may be used tointerconnect the output of logic cells to the input of logic cells toconstruct the semi-custom logic. The logic cells themselves areconstructed by utilizing the first few metal layers to connecttransistors that are built in the silicon substrate. Usually the metal 1layer and metal 2 layer are used for the construction of the logiccells. Sometimes it is effective to also use metal 3 or a part of it.

FIG. 5A is a drawing illustration of inverter 504 with an input 502 andan output 506. An inverter is the simplest logic cell. The input 502 andthe output 506 might be connected to strips in the configurableinterconnection structure.

FIG. 5B is a drawing illustration of a buffer 514 with an input 512 andan output 516. The input 512 and the output 516 might be connected tostrips in the configurable interconnection structure.

FIG. 5C is a drawing illustration of a configurable strength buffer 524with an input 522 and an output 526. The input 522 and the output 526might be connected to strips in the configurable interconnectionstructure. 524 is configurable by means of antifuses 528-1, 528-2 and528-3 constructing an antifuse configurable drive cell.

FIG. 5D is a drawing illustration of D-Flip Flop 534 with inputs 532-2,and output 536 with control inputs 532-1, 532-3, 532-4 and 532-5. Thecontrol signals could be connected to the configurable interconnects orto local or global control signals.

FIG. 6 is a drawing illustration of a LUT 4. LUT4 604 is a well-knownlogic element in the FPGA art called a 16 bit Look-Up-Table or in shortLUT4. It has 4 inputs 602-1, 602-2, 602-3 and 602-4. It has an output606. In general a LUT4 can be programmed to perform any logic functionof 4 inputs or less. The LUT function of FIG. 6 may be implemented by 32antifuses such as 608-1. 604-5 is a two to one multiplexer. The commonway to implement a LUT4 in FPGA is by using 16 SRAM bit-cells and 15multiplexers. The illustration of FIG. 6 demonstrates an antifuseconfigurable look-up-table implementation of a LUT4 by 32 antifuses and7 multiplexers. The programmable cell of FIG. 6 may comprise additionalinputs 602-6, 602-7 with additional 8 antifuse for each input to allowsome functionality in addition to just LUT4.

FIG. 6A is a drawing illustration of a PLA logic cell 6A00. This used tobe the most popular programmable logic primitive until LUT logic tookthe leadership. Other acronyms used for this type of logic are PLD andPAL. 6A01 is one of the antifuses that enables the selection of thesignal fed to the multi-input AND 6A14. In this drawing any crossbetween vertical line and horizontal line comprises an antifuse to allowthe connection to be made according to the desired end function. Thelarge AND cell 6A14 constructs the product term by performing the ANDfunction on the selection of inputs 6A02 or their inverted replicas. Amulti-input OR 6A15 performs the OR function on a selection of thoseproduct terms to construct an output 6A06. FIG. 6A illustrates anantifuse configurable PLA logic.

The logic cells presented in FIG. 5, FIG. 6 and FIG. 6A are justrepresentatives. There exist many options for construction ofprogrammable logic fabric including additional logic cells such as AND,MUX and many others, and variations on those cells. Also, in theconstruction of the logic fabric there might be variation with respectto which of their inputs and outputs are connected by the configurableinterconnect fabric and which are connected directly in anon-configurable way.

FIG. 7 is a drawing illustration of a programmable cell 700. By tilingsuch cells a programmable fabric is constructed. The tiling could be ofthe same cell being repeated over and over to form a homogenous fabric.Alternatively, a blend of different cells could be tiled forheterogeneous fabric. The logic cell 700 could be any of those presentedin FIGS. 5 and 6, a mix and match of them or other primitives asdiscussed before. The logic cell 710 inputs 702 and output 706 areconnected to the configurable interconnection fabric 720 with input andoutput strips 708 with associated antifuses 701. The short interconnects722 are comprising metal strips that are the length of the tile, theycomprise horizontal strips 722H, on one metal layer and vertical strips722V on another layer, with antifuse 701HV in the cross between them, toallow selectively connecting horizontal strip to vertical strip. Theconnection of a horizontal strip to another horizontal strip is withantifuse 701HH that functions like antifuse 410 of FIG. 4. Theconnection of a vertical strip to another vertical strip is withantifuse 701VV that functions like fuse 406 of FIG. 4. The longhorizontal strips 724 are used to route signals that travel a longerdistance, usually the length of 8 or more tiles. Usually one strip ofthe long bundle will have a selective connection by antifuse 724LH tothe short strips, and similarly, for the vertical long strips 724. FIG.7 illustrates the programmable cell 700 as a two dimensionalillustration. In real life 700 is a three dimensional construct wherethe logic cell 710 utilizes the base silicon with Metal 1, Metal 2, andsometimes Metal 3. The programmable interconnect fabric including theassociated antifuses will be constructed on top of it.

FIG. 8 is a drawing illustration of a programmable device layersstructure according to an alternative of the present invention. In thisalternative there are two layers comprising antifuses. The first isdesignated to configure the logic terrain and, in some cases, to alsoconfigure the logic clock distribution. The first antifuse layer couldalso be used to manage some of the power distribution to save power bynot providing power to unused circuits. This layer could also be used toconnect some of the long routing tracks and/or connections to the inputsand outputs of the logic cells.

The device fabrication of the example shown in FIG. 8 starts with thesemiconductor substrate 802 comprising the transistors used for thelogic cells and also the first antifuse layer programming transistors.Then comes layers 804 comprising Metal 1, dielectric, Metal 2, andsometimes Metal 3. These layers are used to construct the logic cellsand often I/O and other analog cells. In this alternative of the presentinvention a plurality of first antifuses are incorporated in theisolation layer between metal 1 and metal 2 or in the isolation layerbetween metal 2 and metal 3 and their programming transistors could beembedded in the silicon substrate 802 being underneath the firstantifuses. These first antifuses could be used to program logic cellssuch as 520, 600 and 700 and to connect individual cells to constructlarger logic functions. These first antifuses could also be used toconfigure the logic clock distribution. The first antifuse layer couldalso be used to manage some of the power distribution to save power bynot providing power to unused circuits. This layer could also be used toconnect some of the long routing tracks and/or one or more connectionsto the inputs and outputs of the cells.

The following few layers 806 could comprise long interconnection tracksfor power distribution and clock networks, or a portion of these, inaddition to what was fabricated in the first few layers 804.

The following few layers 807 could comprise the antifuse configurableinterconnection fabric. It might be called the short interconnectionfabric, too. If metal 6 and metal 7 are used for the strips of thisconfigurable interconnection fabric then the second antifuse may beembedded in the dielectric layer between metal 6 and metal 7.

The programming transistors and the other parts of the programmingcircuit could be fabricated afterward and be on top of the configurableinterconnection fabric 810. The programming element could be a thin filmtransistor or other alternatives for over oxide transistors as wasmentioned previously. In such case the antifuse programming transistorsare placed over the antifuse layer, which may thereby enable theconfigurable interconnect 808 or 804. It should be noted that in somecases it might be useful to construct part of the control logic for thesecond antifuse programming circuits, in the base layers 802 and 804.

The final step is the connection to the outside 812. These could be padsfor wire bonding, soldering balls for flip chip, optical, or otherconnection structures such as those for TSV.

In another alternative of the present invention the antifuseprogrammable interconnect structure could be designed for multiple use.The same structure could be used as a part of the interconnectionfabric, or as a part of the PLA logic cell, or as part of a Read OnlyMemory (ROM) function. In an FPGA product it might be desirable to havean element that could be used for multiple purposes. Having resourcesthat could be used for multiple functions could increase the utility ofthe FPGA device.

FIG. 8A is a drawing illustration of a programmable device layersstructure according to another alternative of the present invention. Inthis alternative there is additional circuit 814 connected by contactconnection 816 to the first antifuse layer 804. This underlying deviceis providing the programming transistor for the first antifuse layer804. In this way, the programmable device substrate diffusion layer 816is not prone to the cost penalty of the programming transistors for thefirst antifuse layer 804. Accordingly the programming connection of thefirst antifuse layer 804 will be directed downward to connect to theunderlying programming device 814 while the programming connection tothe second antifuse layer 807 will be directed upward to connect to theprogramming circuits 810. This could provide less congestion of thecircuit internal interconnection routes.

The reference 808 in subsequent figures can be any one of a vast numberof combinations of possible preprocessed wafers or layers containingmany combinations of transfer layers that fall within the scope of thepresent invention. The term “preprocessed wafer or layer” may be genericand reference number 808 when used in a drawing figure to illustrate anembodiment of the present invention may represent many differentpreprocessed wafer or layer types including but not limited tounderlying prefabricated layers, a lower layer interconnect wiring, abase layer, a substrate layer, a processed house wafer, an acceptorwafer, a logic house wafer, an acceptor wafer house, an acceptorsubstrate, target wafer, preprocessed circuitry, a preprocessedcircuitry acceptor wafer, a base wafer layer, a lower layer, anunderlying main wafer, a foundation layer, an attic layer, or a housewafer.

FIG. 8B is a drawing illustration of a generalized preprocessed wafer orlayer 808. The wafer or layer 808 may have preprocessed circuitry, suchas, for example, logic circuitry, microprocessors, circuitry comprisingtransistors of various types, and other types of digital or analogcircuitry including, but not limited to, the various embodimentsdescribed herein. Preprocessed wafer or layer 808 may have preprocessedmetal interconnects and may be comprised of copper or aluminum. Themetal layer or layers of interconnect may be constructed of lower (lessthan approximately 400° C.) thermal damage resistant metals such as, forexample, copper or aluminum, or may be constructed with refractorymetals such as tungsten to provide high temperature utility at greaterthan approximately 400° C. The preprocessed metal interconnects may bedesigned and prepared for layer transfer and electrical coupling frompreprocessed wafer or layer 808 to the layer or layers to betransferred.

FIG. 8C is a drawing illustration of a generalized transfer layer 809prior to being attached to preprocessed wafer or layer 808. Transferlayer 809 may be attached to a carrier wafer or substrate during layertransfer. Preprocessed wafer or layer 808 may be called a target wafer,acceptor substrate, or acceptor wafer. The acceptor wafer may haveacceptor wafer metal connect pads or strips designed and prepared forelectrical coupling to transfer layer 809. Transfer layer 809 may beattached to a carrier wafer or substrate during layer transfer. Transferlayer 809 may have metal interconnects designed and prepared for layertransfer and electrical coupling to preprocessed wafer or layer 808. Themetal interconnects now on transfer layer 809 may be comprised of copperor aluminum. Electrical coupling from transferred layer 809 topreprocessed wafer or layer 808 may utilize thru layer vias (TLVs) asthe connection path. Transfer layer 809 may be comprised of singlecrystal silicon, or mono-crystalline silicon, or doped mono-crystallinelayer or layers, or other semiconductor, metal, and insulator materials,layers; or multiple regions of single crystal silicon, ormono-crystalline silicon, or dope mono-crystalline silicon, or othersemiconductor, metal, or insulator materials.

FIG. 8D is a drawing illustration of a preprocessed wafer or layer 808Acreated by the layer transfer of transfer layer 809 on top ofpreprocessed wafer or layer 808. The top of preprocessed wafer or layer808A may be further processed with metal interconnects designed andprepared for layer transfer and electrical coupling from preprocessedwafer or layer 808A to the next layer or layers to be transferred.

FIG. 8E is a drawing illustration of a generalized transfer layer 809Aprior to being attached to preprocessed wafer or layer 808A. Transferlayer 809A may be attached to a carrier wafer or substrate during layertransfer. Transfer layer 809A may have metal interconnects designed andprepared for layer transfer and electrical coupling to preprocessedwafer or layer 808A.

FIG. 8F is a drawing illustration of a preprocessed wafer or layer 808Bcreated by the layer transfer of transfer layer 809A on top ofpreprocessed wafer or layer 808A. The top of preprocessed wafer or layer808B may be further processed with metal interconnects designed andprepared for layer transfer and electrical coupling from preprocessedwafer or layer 808B to the next layer or layers to be transferred.

FIG. 8G is a drawing illustration of a generalized transfer layer 809Bprior to being attached to preprocessed wafer or layer 808B. Transferlayer 809B may be attached to a carrier wafer or substrate during layertransfer. Transfer layer 809B may have metal interconnects designed andprepared for layer transfer and electrical coupling to preprocessedwafer or layer 808B.

FIG. 8H is a drawing illustration of preprocessed wafer layer 808Ccreated by the layer transfer of transfer layer 809B on top ofpreprocessed wafer or layer 808B. The top of preprocessed wafer or layer808C may be further processed with metal interconnect designed andprepared for layer transfer and electrical coupling from preprocessedwafer or layer 808C to the next layer or layers to be transferred.

FIG. 8I is a drawing illustration of preprocessed wafer or layer 808C, a3D IC stack, which may comprise transferred layers 809A and 809B on topof the original preprocessed wafer or layer 808. Transferred layers 809Aand 809B and the original preprocessed wafer or layer 808 may comprisetransistors of one or more types in one or more layers, metallizationsuch as, for example, copper or aluminum in one or more layers,interconnections to and between layers above and below, andinterconnections within the layer. The transistors may be of varioustypes that may be different from layer to layer or within the samelayer. The transistors may be in various organized patterns. Thetransistors may be in various pattern repeats or bands. The transistorsmay be in multiple layers involved in the transfer layer. Thetransistors may be junction-less transistors or recessed channel arraytransistors. Transferred layers 809A and 809B and the originalpreprocessed wafer or layer 808 may further comprise semiconductordevices such as resistors and capacitors and inductors, one or moreprogrammable interconnects, memory structures and devices, sensors,radio frequency devices, or optical interconnect with associatedtransceivers. The terms carrier wafer or carrier substrate may also becalled holder wafer or holder substrate.

This layer transfer process can be repeated many times, thereby creatingpreprocessed wafers comprising many different transferred layers which,when combined, can then become preprocessed wafers or layers for futuretransfers. This layer transfer process may be sufficiently flexible thatpreprocessed wafers and transfer layers, if properly prepared, can beflipped over and processed on either side with further transfers ineither direction as a matter of design choice.

The thinner the transferred layer, the smaller the thru layer viadiameter obtainable, due to the limitations of manufacturable via aspectratios. Thus, the transferred layer may be, for example, less than 2microns thick, less than 1 micron thick, less than 0.4 microns thick,less than 200 nm thick, or less than 100 nm thick. The thickness of thelayer or layers transferred according to some embodiments of the presentinvention may be designed as such to match and enable the bestobtainable lithographic resolution capability of the manufacturingprocess employed to create the thru layer vias or any other structureson the transferred layer or layers.

In many of the embodiments of the present invention, the layer or layerstransferred may be of mono-crystalline silicon, and after layertransfer, further processing, such as, for example, plasma/RIE or wetetching, may be done on the layer or layers that may create islands ormesas of the transferred layer or layers of mono-crystalline silicon,the crystal orientation of which has not changed. Thus, amono-crystalline layer or layers of a certain specific crystalorientation may be layer transferred and then processed whereby theresultant islands or mesas of mono-crystalline silicon have the samecrystal specific orientation as the layer or layers before theprocessing.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 8 through 8I are exemplary only and are not drawnto scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the preprocessed wafer orlayer 808 may act as a base or substrate layer in a wafer transfer flow,or as a preprocessed or partially preprocessed circuitry acceptor waferin a wafer transfer process flow. Many other modifications within thescope of the present invention will suggest themselves to such skilledpersons after reading this specification. Thus the invention is to belimited only by the appended claims.

An alternative technology for such underlying circuitry is to use the“SmartCut” process. The “SmartCut” process is a well understoodtechnology used for fabrication of SOI wafers. The “SmartCut” process,together with wafer bonding technology, enables a “Layer Transfer”whereby a thin layer of a single or mono-crystalline silicon wafer istransferred from one wafer to another wafer. The “Layer Transfer” couldbe done at less than 400° C. and the resultant transferred layer couldbe even less than 100 nm thick. The process with some variations andunder different names is commercially available by two companies,namely, Soitec (Crolles, France) and SiGen—Silicon Genesis Corporation(San Jose, Calif.). A room temperature wafer bonding process utilizingion-beam preparation of the wafer surfaces in a vacuum has been recentlydemonstrated by Mitsubishi Heavy Industries Ltd., Tokyo, Japan. Thisprocess allows room temperature layer transfer.

Alternatively, other technology may also be used. For example, othertechnologies may be utilized for layer transfer as described in, forexample, IBM's layer transfer method shown at IEDM 2005 by A. W. Topol,et. al. The IBM's layer transfer method employs a SOI technology andutilizes glass handle wafers. The donor circuit may be high-temperatureprocessed on an SOI wafer, temporarily bonded to a borosilicate glasshandle wafer, backside thinned by chemical mechanical polishing of thesilicon and then the Buried Oxide (BOX) is selectively etched off. Thenow thinned donor wafer is subsequently aligned and low-temperatureoxide-to-oxide bonded to the acceptor wafer topside. A low temperaturerelease of the glass handle wafer from the thinned donor wafer isperformed, and then thru bond via connections are made. Additionally,epitaxial liftoff (ELO) technology as shown by P. Demeester, et. al, ofIMEC in Semiconductor Science Technology 1993 may be utilized for layertransfer. ELO makes use of the selective removal of a very thinsacrificial layer between the substrate and the layer structure to betransferred. The to-be-transferred layer of GaAs or silicon may beadhesively ‘rolled’ up on a cylinder or removed from the substrate byutilizing a flexible carrier, such as, for example, black wax, to bow upthe to-be-transferred layer structure when the selective etch, such as,for example, diluted Hydrofluoric (HF) Acid, etches the exposed releaselayer, such as, for example, silicon oxide in SOI or AlAs. Afterliftoff, the transferred layer is then aligned and bonded to theacceptor substrate or wafer. The manufacturability of the ELO processfor multilayer layer transfer use was recently improved by J. Yoon, et.al., of the University of Illinois at Urbana-Champaign as described inNature May 20, 2010. Canon developed a layer transfer technology calledELTRAN—Epitaxial Layer TRANsfer from porous silicon. ELTRAN may beutilized. The Electrochemical Society Meeting abstract No. 438 from year2000 and the JSAP International July 2001 paper show a seed wafer beinganodized in an HF/ethanol solution to create pores in the top layer ofsilicon, the pores are treated with a low temperature oxidation and thenhigh temperature hydrogen annealed to seal the pores. Epitaxial siliconmay then be deposited on top of the porous silicon and then oxidized toform the SOI BOX. The seed wafer may be bonded to a handle wafer and theseed wafer may be split off by high pressure water directed at theporous silicon layer. The porous silicon may then be selectively etchedoff leaving a uniform silicon layer.

FIG. 14 is a drawing illustration of a layer transfer process flow. Inanother embodiment of the present invention, “Layer-Transfer” is usedfor construction of the underlying circuitry 814. 1402 is a wafer thatwas processed to construct the underlying circuitry. The wafer 1402could be of the most advanced process or more likely a few generationsbehind. It could comprise the programming circuits 814 and other usefulstructures and may be a preprocessed CMOS silicon wafer, or a partiallyprocessed CMOS, or other prepared silicon or semiconductor substrate.Wafer 1402 may also be called an acceptor substrate or a target wafer.An oxide layer 1412 is then deposited on top of the wafer 1402 and thenis polished for better planarization and surface preparation. A donorwafer 1406 is then brought in to be bonded to 1402. The surfaces of bothdonor wafer 1406 and wafer 1402 may be pre-processed for low temperaturebonding by various surface treatments, such as an RCA pre-clean that maycomprise dilute ammonium hydroxide or hydrochloric acid, and may includeplasma surface preparations to lower the bonding energy and enhance thewafer to wafer bond strength. The donor wafer 1406 is pre-prepared for“SmartCut” by an ion implant of an atomic species, such as H+ ions, atthe desired depth to prepare the SmartCut line 1408. SmartCut line 1408may also be called a layer transfer demarcation plane, shown as a dashedline. The SmartCut line 1408 or layer transfer demarcation plane may beformed before or after other processing on the donor wafer 1406. Donorwafer 1406 may be bonded to wafer 1402 by bringing the donor wafer 1406surface in physical contact with the wafer 1402 surface, and thenapplying mechanical force and/or thermal annealing to strengthen theoxide to oxide bond. Alignment of the donor wafer 1406 with the wafer1402 may be performed immediately prior to the wafer bonding. Acceptablebond strengths may be obtained with bonding thermal cycles that do notexceed approximately 400° C. After bonding the two wafers a SmartCutstep is performed to cleave and remove the top portion 1414 of the donorwafer 1406 along the cut layer 1408. The cleaving may be accomplished byvarious applications of energy to the SmartCut line 1408, or layertransfer demarcation plane, such as a mechanical strike by a knife orjet of liquid or jet of air, or by local laser heating, or othersuitable methods. The result is a 3D wafer 1410 which comprises wafer1402 with an added layer 1404 of mono-crystalline silicon, or multiplelayers of materials. Layer 1404 may be polished chemically andmechanically to provide a suitable surface for further processing. Layer1404 could be quite thin at the range of 50-200 nm. The described flowis called “layer transfer”. Layer transfer is commonly utilized in thefabrication of SOI—Silicon On Insulator—wafers. For SOI wafers the uppersurface is oxidized so that after “layer transfer” a buriedoxide—BOX—provides isolation between the top thin mono-crystallinesilicon layer and the bulk of the wafer. The use of an implanted atomicspecies, such as Hydrogen or Helium or a combination, to create acleaving plane as described above may be referred to in this document as“ion-cut” and is generally the illustrated layer transfer method.

Persons of ordinary skill in the art will appreciate that theillustrations in FIG. 14 are exemplary only and are not drawn to scale.Such skilled persons will further appreciate that many variations arepossible such as, for example, a heavily doped (greater than 1e20atoms/cm3) boron layer or silicon germanium (SiGe) layer may be utilizedas an etch stop either within the ion-cut process flow, wherein thelayer transfer demarcation plane may be placed within the etch stoplayer or into the substrate material below, or the etch stop layers maybe utilized without an implant cleave process and the donor wafer may bepreferentially etched away until the etch stop layer is reached. Suchskilled persons will further appreciate that the oxide layer within anSOI or GeOI donor wafer may serve as the etch stop layer, and hence oneedge of the oxide layer may function as a layer transfer demarcationplane. Many other modifications within the scope of the invention willsuggest themselves to such skilled persons after reading thisspecification. Thus the invention is to be limited only by the appendedclaims.

Now that a “layer transfer” process is used to bond a thinmono-crystalline silicon layer 1404 on top of the preprocessed wafer1402, a standard process could ensue to construct the rest of thedesired circuits as is illustrated in FIG. 8A, starting with layer 802on the transferred layer 1404. The lithography step will use alignmentmarks on wafer 1402 so the following circuits 802 and 816 and so forthcould be properly connected to the underlying circuits 814. An aspectthat should be accounted for is the high temperature that would beneeded for the processing of circuits 802. The pre-processed circuits onwafer 1402 would need to withstand this high temperature needed for theactivation of the semiconductor transistors 802 fabricated on the 1404layer. Those circuits on wafer 1402 will comprise transistors and localinterconnects of poly-crystalline silicon (polysilicon or poly) and someother type of interconnection that could withstand high temperature suchas tungsten. A processed wafer that can withstand subsequent processingof transistors on top at high temperatures may be a called the“Foundation” or a foundation wafer, layer or circuitry. An advantage ofusing layer transfer for the construction of the underlying circuits ishaving the layer transferred 1404 be very thin which enables the throughsilicon via connections 816, or thru layer vias (TLVs), to have lowaspect ratios and be more like normal contacts, which could be made verysmall and with minimum area penalty. The thin transferred layer alsoallows conventional direct thru-layer alignment techniques to beperformed, thus increasing the density of silicon via connections 816.

FIG. 15 is a drawing illustration of an underlying programming circuit.Programming Transistors 1501 and 1502 are pre-fabricated on thefoundation wafer 1402 and then the programmable logic circuits and theantifuse 1504 are built on the transferred layer 1404. The programmingconnections 1506, 1508 are connected to the programming transistors bycontact holes through layer 1404 as illustrated in FIG. 8A by 816. Theprogramming transistors are designed to withstand the relatively higherprogramming voltage for the antifuse 1504 programming.

FIG. 16 is a drawing illustration of an underlying isolation transistorcircuit. The higher voltage used to program the antifuse 1604 mightdamage the logic transistors 1606, 1608. To protect the logic circuits,isolation transistors 1601, 1602, which are designed to withstand highervoltage, are used. The higher programming voltage is only used at theprogramming phase at which time the isolation transistors are turned offby the control circuit 1603. The underlying wafer 1402 could also beused to carry the isolation transistors. Having the relatively largeprogramming transistors and isolation transistor on the foundationsilicon 1402 allows far better use of the primary silicon 802 (1404).Usually the primary silicon will be built in an advanced process toprovide high density and performance. The foundation silicon could bebuilt in a less advanced process to reduce costs and support the highervoltage transistors. It could also be built with other than CMOStransistors such as Double Diffused Metal Oxide Semiconductor (DMOS) orbi-polar junction transistors when such is advantageous for theprogramming and the isolation function. In many cases there is a need tohave protection diodes for the gate input that are called Antennas. Suchprotection diodes could be also effectively integrated in the foundationalongside the input related Isolation Transistors. On the other hand theisolation transistors 1601, 1602 would provide the protection for theantenna effect so no additional diodes would be needed.

An additional alternative embodiment of the present invention is wherethe foundation layer 1402 is pre-processed to carry a plurality of backbias voltage generators. A known challenge in advanced semiconductorlogic devices is die-to-die and within-a-die parameter variations.Various sites within the die might have different electricalcharacteristics due to dopant variations and such. The most critical ofthese parameters that affect the variation is the threshold voltage ofthe transistor. Threshold voltage variability across the die is mainlydue to channel dopant, gate dielectric, and critical dimensionvariability. This variation becomes profound in sub 45 nm node devices.The usual implication is that the design should be done for the worstcase, resulting in a quite significant performance penalty.Alternatively complete new designs of devices are being proposed tosolve this variability problem with significant uncertainty in yield andcost. A possible solution is to use localized back bias to drive upwardthe performance of the worst zones and allow better overall performancewith minimal additional power. The foundation-located back bias couldalso be used to minimize leakage due to process variation.

FIG. 17A is a topology drawing illustration of back bias circuitry. Thefoundation layer 1402 carries back bias circuits 1711 to allow enhancingthe performance of some of the zones 1710 on the primary device whichotherwise will have lower performance.

FIG. 17B is a drawing illustration of back bias circuits. A back biaslevel control circuit 1720 is controlling the oscillators 1727 and 1729to drive the voltage generators 1721. The negative voltage generator1725 will generate the desired negative bias which will be connected tothe primary circuit by connection 1723 to back bias the N-channelMetal-Oxide-Semiconductor (NMOS) transistors 1732 on the primary silicon1404. The positive voltage generator 1726 will generate the desirednegative bias which will be connected to the primary circuit byconnection 1724 to back bias the P-channel Metal-Oxide-Semiconductor(PMOS) transistors 1724 on the primary silicon 1404. The setting of theproper back bias level per zone will be done in the initiation phase. Itcould be done by using external tester and controller or by on-chip selftest circuitry. Preferably a non volatile memory will be used to storethe per zone back bias voltage level so the device could be properlyinitialized at power up. Alternatively a dynamic scheme could be usedwhere different back bias level(s) are used in different operating modesof the device. Having the back bias circuitry in the foundation allowsbetter utilization of the primary device silicon resources and lessdistortion for the logic operation on the primary device.

FIG. 17C illustrates an alternative circuit function that may fit wellin the “Foundation.” In many IC designs it is desired to integrate powercontrol to reduce either voltage to sections of the device or to totallypower off these sections when those sections are not needed or in analmost ‘sleep’ mode. In general such power control is best done withhigher voltage transistors. Accordingly a power control circuit cell17C02 may be constructed in the Foundation. Such power control 17C02 mayhave its own higher voltage supply and control or regulate supplyvoltage for sections 17C10 and 17C08 in the “Primary” device. Thecontrol may come from the primary device 17C16 and be managed by controlcircuit 17C04 in the Foundation.

FIG. 17D illustrates an alternative circuit function that may fit wellin the “Foundation.” In many IC designs it is desired to integrate aprobe auxiliary system that will make it very easy to probe the devicein the debugging phase, and to support production testing. Probecircuits have been used in the prior art sharing the same transistorlayer as the primary circuit. FIG. 17D illustrates a probe circuitconstructed in the Foundation underneath the active circuits in theprimary layer. FIG. 17D illustrates that the connections are made to thesequential active circuit elements 17D02. Those connections are routedto the Foundation through interconnect lines 17D06 where high impedanceprobe circuits 17D08 will be used to sense the sequential elementoutput. A selector circuit 17D12 allows one or more of those sequentialoutputs to be routed out through one or more buffers 17D16 which may becontrolled by signals from the Primary circuit to supply the drive ofthe sequential output signal to the probed signal output 17D14 fordebugging or testing. Persons of ordinary skill in the art willappreciate that other configurations are possible like, for example,having multiple groups of probe circuitry 17D08, multiple probe outputsignals 17D14, and controlling buffers 17D16 with signals notoriginating in the primary circuit.

In another alternative the foundation substrate 1402 could additionallycarry SRAM cells as illustrated in FIG. 18. The SRAM cells 1802pre-fabricated on the underlying substrate 1402 could be connected 1812to the primary logic circuit 1806, 1808 built on 1404. As mentionedbefore, the layers built on 1404 could be aligned to the pre-fabricatedstructure on the underlying substrate 1402 so that the logic cells couldbe properly connected to the underlying RAM cells.

FIG. 19A is a drawing illustration of an underlying I/O. The foundation1402 could also be preprocessed to carry the I/O circuits or part of it,such as the relatively large transistors of the output drive 1912.Additionally TSV in the foundation could be used to bring the I/Oconnection 1914 all the way to the back side of the foundation. FIG. 19Bis a drawing illustration of a side “cut” of an integrated deviceaccording to an embodiment of the present invention. The Output Driveris illustrated by PMOS and NMOS output transistors 19B06 coupled throughTSV 19B10 to connect to a backside pad or pad bump 19B08. The connectionmaterial used in the foundation 1402 can be selected to withstand thetemperature of the following process constructing the full device on1404 as illustrated in FIG. 8A—802, 804, 806, 807, 810, 812, such astungsten. The foundation could also carry the input protection circuit1916 connecting the pad 19B08 to the input logic 1920 in the primarycircuits.

An additional embodiment of the present invention may be to use TSVs inthe foundation such as TSV 19B10 to connect between wafers to form 3DIntegrated Systems. In general each TSV takes a relatively large area,typically a few square microns. When the need is for many TSVs, theoverall cost of the area for these TSVs might be high if the use of thatarea for high density transistors is precluded. Pre-processing theseTSVs on the donor wafer on a relatively older process line willsignificantly reduce the effective costs of the 3D TSV connections. Theconnection 1924 to the primary silicon circuitry 1920 could be then madeat the minimum contact size of few tens of square nanometers, which istwo orders of magnitude lower than the few square microns needed by theTSVs. Those of ordinary skill in the art will appreciate that FIG. 19Bis for illustration only and is not drawn to scale. Such skilled personswill understand there are many alternative embodiments and componentarrangements that could be constructed using the inventive principlesshown and that FIG. 19B is not limiting in any way.

FIG. 19C demonstrates a 3D system comprising three dice 19C10, 19C20 and19C30 coupled together with TSVs 19C12, 19C22 and 19C32 similar to TSV19B10 as described in association with FIG. 19A. The stack of three diceutilize TSV in the Foundations 19C12, 19C22, and 19C32 for the 3Dinterconnect may allow for minimum effect or silicon area loss of thePrimary silicon 19C14, 19C24 and 19C34 connected to their respectiveFoundations with minimum size via connections. The three die stacks maybe connected to a PC Board using bumps 19C40 connected to the bottom dieTSVs 19C32. Those of ordinary skill in the art will appreciate that FIG.19C is for illustration only and is not drawn to scale. Such skilledpersons will understand there are many alternative embodiments andcomponent arrangements that could be constructed using the inventiveprinciples shown and that FIG. 19C is not limiting in any way. Forexample, a die stack could be placed in a package using flip chipbonding or the bumps 19C40 could be replaced with bond pads and the partflipped over and bonded in a conventional package with bond wires.

FIG. 19D illustrates a 3D IC processor and DRAM system. A well knownproblem in the computing industry is known as the “memory wall” andrelates to the speed the processor can access the DRAM. The prior artproposed solution was to connect a DRAM stack using TSV directly on topof the processor and use a heat spreader attached to the processor backto remove the processor heat. But in order to do so, a special via needsto go “through DRAM” so that the processor I/Os and power could beconnected. Having many processor-related ‘through-DRAM vias” leads to afew severe disadvantages. First, it reduces the usable silicon area ofthe DRAM by a few percent. Second, it increases the power overhead by afew percent. Third, it requires that the DRAM design be coordinated withthe processor design which is very commercially challenging. Theembodiment of FIG. 19D illustrates one solution to mitigate the abovementioned disadvantages by having a foundation with TSVs as illustratedin FIGS. 19B and 19C. The use of the foundation and primary structuremay enable the connections of the processor without going through theDRAM.

In FIG. 19D the processor I/Os and power may be coupled from theface-down microprocessor active area 19D14—the primary layer, by vias19D08 through heat spreader substrate 19D04 to an interposer 19D06. Aheat spreader 19D12, the heat spreader substrate 19D04, and heat sink19D02 are used to spread the heat generated on the processor active area19D14. TSVs 19D22 through the Foundation 19D16 are used for theconnection of the DRAM stack 19D24. The DRAM stack comprises multiplethinned DRAM 19D18 interconnected by TSV 19D20. Accordingly the DRAMstack does not need to pass through the processor I/O and power planesand could be designed and produced independent of the processor designand layout. The DRAM chip 19D18 that is closest to the Foundation 19D16may be designed to connect to the Foundation TSVs 19D22, or a separateReDistribution Layer (or RDL, not shown) may be added in between, or theFoundation 19D16 could serve that function with preprocessed hightemperature interconnect layers, such as Tungsten, as describedpreviously. And the processor's active area is not compromised by havingTSVs through it as those are done in the Foundation 19D16.

Alternatively the Foundation vias 19D22 could be used to pass theprocessor I/O and power to the substrate 19D04 and to the interposer19D06 while the DRAM stack would be coupled directly to the processoractive area 19D14. Persons of ordinary skill in the art will appreciatethat many more combinations are possible within the scope of thedisclosed present invention.

FIG. 19E illustrates another embodiment of the present invention whereinthe DRAM stack 19D24 may be coupled by wire bonds 19E24 to an RDL(ReDistribution Layer) 19E26 that couples the DRAM to the Foundationvias 19D22, and thus couples them to the face-down processor 19D14.

In yet another embodiment, custom SOI wafers are used where NuVias 19F00may be processed by the wafer supplier. NuVias 19F00 may be conventionalTSVs that may be 1 micron or larger in diameter and may be preprocessedby an SOI wafer vendor. This is illustrated in FIG. 19F with handlewafer 19F02 and Buried Oxide BOX 19F01. The handle wafer 19F02 maytypically be many hundreds of microns thick, and the BOX 19F01 maytypically be a few hundred nanometers thick. The Integrated DeviceManufacturer (IDM) or foundry then processes NuContacts 19F03 to connectto the NuVias 19F00. NuContacts may be conventionally dimensionedcontacts etched thru the thin silicon 19F05 and the BOX 19F01 of the SOIand filled with metal. The NuContact diameter DNuContact 19F04, in FIG.19F may then be processed into the tens of nanometer range. The priorart of construction with bulk silicon wafers 19G00 as illustrated inFIG. 19G typically has a TSV diameter, DTSV_prior_art 19G02, in themicron range. The reduced dimension of NuContact DNuContact 19F04 inFIG. 19F may have important implications for semiconductor designers.The use of NuContacts may provide reduced die size penalty ofthrough-silicon connections, reduced handling of very thin siliconwafers, and reduced design complexity. The arrangement of TSVs in customSOI wafers can be based on a high-volume integrated device manufacturer(IDM) or foundry's request, or be based on a commonly agreed industrystandard.

A process flow as illustrated in FIG. 19H may be utilized to manufacturethese custom SOI wafers. Such a flow may be used by a wafer supplier. Asilicon donor wafer 19H04 is taken and its surface 19H05 may beoxidized. An atomic species, such as, for example, hydrogen, may then beimplanted at a certain depth 19H06. Oxide-to-oxide bonding as describedin other embodiments may then be used to bond this wafer with anacceptor wafer 19H08 having pre-processed NuVias 19H07. The NuVias 19H07may be constructed with a conductive material, such as tungsten or dopedsilicon, which can withstand high-temperature processing. An insulatingbarrier, such as, for example, silicon oxide, may be utilized toelectrically isolate the NuVia 19H07 from the silicon of the acceptorwafer 19H08. Alternatively, the wafer supplier may construct NuVias19H07 with silicon oxide. The integrated device manufacturer or foundryetches out this oxide after the high-temperature (more than 400° C.)transistor fabrication is complete and may replace this oxide with ametal such as copper or aluminum. This process may allow a low-meltingpoint, but highly conductive metal, like copper to be used. Followingthe bonding, a portion 19H10 of the donor silicon wafer 19H04 may becleaved at 19H06 and then chemically mechanically polished as describedin other embodiments.

FIG. 19J depicts another technique to manufacture custom SOI wafers. Astandard SOI wafer with substrate 19J01, box 19F01, and top siliconlayer 19J02 may be taken and NuVias 19F00 may be formed from theback-side up to the oxide layer. This technique might have a thickerburied oxide 19F01 than a standard SOI process.

FIG. 19I depicts how a custom SOI wafer may be used for 3D stacking of aprocessor 19I09 and a DRAM 19I10. In this configuration, a processor'spower distribution and I/O connections have to pass from the substrate19I12, go through the DRAM 19I10 and then connect onto the processor19I09. The above described technique in FIG. 19F may result in a smallcontact area on the DRAM active silicon, which is very convenient forthis processor-DRAM stacking application. The transistor area lost onthe DRAM die due to the through-silicon connection 19I13 and 19I14 isvery small due to the tens of nanometer diameter of NuContact 19I13 inthe active DRAM silicon. It is difficult to design a DRAM when largeareas in its center are blocked by large through-silicon connections.Having small size through-silicon connections may help tackle thisissue. Persons of ordinary skill in the art will appreciate that thistechnique may be applied to building processor-SRAM stacks,processor-flash memory stacks, processor-graphics-memory stacks, anycombination of the above, and any other combination of relatedintegrated circuits such as, for example, SRAM-based programmable logicdevices and their associated configuration ROM/PROM/EPROM/EEPROMdevices, ASICs and power regulators, microcontrollers and analogfunctions, etc. Additionally, the silicon on insulator (SOI) may be amaterial such as polysilicon, GaAs, GaN, etc. on an insulator. Suchskilled persons will appreciate that the applications of NuVia andNuContact technology are extremely general and the scope of the presentinvention is to be limited only by the appended claims.

In another embodiment of the present invention the foundation substrate1402 could additionally carry re-drive cells (often called buffers).Re-drive cells are common in the industry for signals which is routedover a relatively long path. As the routing has a severe resistance andcapacitance penalty it is helpful to insert re-drive circuits along thepath to avoid a severe degradation of signal timing and shape. Anadvantage of having re-drivers in the foundation 1402 is that thesere-drivers could be constructed from transistors who could withstand theprogramming voltage. Otherwise isolation transistors such as 1601 and1602 or other isolation scheme may be used at the logic cell input andoutput.

FIG. 8A is a cut illustration of a programmable device, with twoantifuse layers. The programming transistors for the first one 804 couldbe prefabricated on 814, and then, utilizing “smart-cut”, a singlecrystal, or mono-crystalline, silicon layer 1404 is transferred on whichthe primary programmable logic 802 is fabricated with advanced logictransistors and other circuits. Then multi-metal layers are fabricatedincluding a lower layer of antifuses 804, interconnection layers 806 andsecond antifuse layer with its configurable interconnects 807. For thesecond antifuse layer the programming transistors 810 could befabricated also utilizing a second “smart-cut” layer transfer.

FIG. 20 is a drawing illustration of the second layer transfer processflow. The primary processed wafer 2002 comprises all the priorlayers—814, 802, 804, 806, and 807. An oxide layer 2012 is thendeposited on top of the wafer 2002 and then polished for betterplanarization and surface preparation. A donor wafer 2006 (or cleavablewafer as labeled in the drawing) is then brought in to be bonded to2002. The donor wafer 2006 is pre processed to comprise thesemiconductor layers 2019 which will be later used to construct the toplayer of programming transistors 810 as an alternative to the TFTtransistors. The donor wafer 2006 is also prepared for “SmartCut” by ionimplant of an atomic species, such as H+, at the desired depth toprepare the SmartCut line 2008. After bonding the two wafers a SmartCutstep is performed to pull out the top portion 2014 of the donor wafer2006 along the cut layer 2008. This donor wafer may now also beprocessed and reused for more layer transfers. The result is a 3D wafer2010 which comprises wafer 2002 with an added layer 2004 of singlecrystal silicon pre-processed to carry additional semiconductor layers.The transferred slice 2004 could be quite thin at the range of 10-200nm. Utilizing “SmartCut” layer transfer provides single crystalsemiconductors layer on top of a pre-processed wafer without heating thepre-processed wafer to more than 400° C.

There are a few alternative methods to construct the top transistorsprecisely aligned to the underlying pre-fabricated layers such aspre-processed wafer or layer 808, utilizing “SmartCut” layer transferand not exceeding the temperature limit, typically approximately 400°C., of the underlying pre-fabricated structure, which may include lowmelting temperature metals or other construction materials such as, forexample, aluminum or copper. As the layer transfer is less than 200 nmthick, then the transistors defined on it could be aligned precisely tothe top metal layer of the pre-processed wafer or layer 808 as may beneeded and those transistors have less than 40 nm misalignment as wellas thru layer via, or layer to layer metal connection, diameters of lessthan 50 nm. The thinner the transferred layer, the smaller the thrulayer via diameter obtainable, due to the limitations of manufacturablevia aspect ratios. Thus, the transferred layer may be, for example, lessthan 2 microns thick, less than 1 micron thick, less than 0.4 micronsthick, less than 200 nm thick, or less than 100 nm thick.

One alternative method is to have a thin layer transfer of singlecrystal silicon which will be used for epitaxial Ge crystal growth usingthe transferred layer as the seed for the germanium. Another alternativemethod is to use the thin layer transfer of mono-crystalline silicon forepitaxial growth of GexSi1-x. The percent Ge in Silicon of such layerwould be determined by the transistor specifications of the circuitry.Prior art have presented approaches whereby the base silicon is used tocrystallize the germanium on top of the oxide by using holes in theoxide to drive crystal or lattice seeding from the underlying siliconcrystal. However, it is very hard to do such on top of multipleinterconnection layers. By using layer transfer we can have amono-crystalline layer of silicon crystal on top and make it relativelyeasy to seed and crystallize an overlying germanium layer. Amorphousgermanium could be conformally deposited by CVD at 300° C. and patternaligned to the underlying layer, such as the pre-processed wafer orlayer 808, and then encapsulated by a low temperature oxide. A shortmicros-duration heat pulse melts the Ge layer while keeping theunderlying structure below 400° C. The Ge/Si interface will start thecrystal or lattice epitaxial growth to crystallize the germanium orGexSi1-x layer. Then implants are made to form Ge transistors andactivated by laser pulses without damaging the underlying structuretaking advantage of the low activation temperature of dopants ingermanium.

Another alternative method is to preprocess the wafer used for layertransfer as illustrated in FIG. 21. FIG. 21A is a drawing illustrationof a pre-processed wafer used for a layer transfer. A lightly dopedP-type wafer (P− wafer) 2102 may be processed to have a “buried” layerof highly doped N-type silicon (N+) 2104, by implant and activation, orby shallow N+ implant and diffusion followed by a P− epi growth(epitaxial growth) 2106. Optionally, if a substrate contact is neededfor transistor performance, an additional shallow P+ layer 2108 isimplanted and activated. FIG. 21B is a drawing illustration of thepre-processed wafer made ready for a layer transfer by an implant of anatomic species, such as H+, preparing the SmartCut “cleaving plane” 2110in the lower part of the N+ region and an oxide deposition or growth2112 in preparation for oxide to oxide bonding. Now alayer-transfer-flow should be performed to transfer the pre-processedsingle crystal P− silicon with N+ layer, on top of pre-processed waferor layer 808. The top of pre-processed wafer or layer 808 may beprepared for bonding by deposition of an oxide, or surface treatments,or both. Persons of ordinary skill in the art will appreciate that theprocessing methods presented above are illustrative only and that otherembodiments of the inventive principles described herein are possibleand thus the scope if the invention is only limited by the appendedclaims.

FIGS. 22A-22H are drawing illustrations of the formation of planar topsource extension transistors. FIG. 22A illustrates the layer transferredon top of preprocessed wafer or layer 808 after the smart cut whereinthe N+ 2104 is on top. Then the top transistor source 22B04 and drain22B06 are defined by etching away the N+ from the region designated forgates 22B02, leaving a thin more lightly doped N+ layer for the futuresource and drain extensions, and the isolation region betweentransistors 22B08. Utilizing an additional masking layer, the isolationregion 22B08 is defined by an etch all the way to the top ofpre-processed wafer or layer 808 to provide full isolation betweentransistors or groups of transistors. Etching away the N+ layer betweentransistors is helpful as the N+ layer is conducting. This step isaligned to the top of the pre-processed wafer or layer 808 so that theformed transistors could be properly connected to metal layers of thepre-processed wafer or layer 808. Then a highly conformalLow-Temperature Oxide 22C02 (or Oxide/Nitride stack) is deposited andetched resulting in the structure illustrated in FIG. 22C. FIG. 22Dillustrates the structure following a self-aligned etch step preparationfor gate formation 22D02, thereby forming the source and drainextensions 22D04. FIG. 22E illustrates the structure following a lowtemperature microwave oxidation technique, such as the TEL SPA (TokyoElectron Limited Slot Plane Antenna) oxygen radical plasma, that growsor deposits a low temperature Gate Dielectric 22E02 to serve as theMOSFET gate oxide, or an atomic layer deposition (ALD) technique may beutilized. Alternatively, the gate structure may be formed by a high kmetal gate process flow as follows. Following an industry standardHF/SC1/SC2 clean to create an atomically smooth surface, a high-kdielectric 22E02 is deposited. The semiconductor industry has chosenHafnium-based dielectrics as the leading material of choice to replaceSiO2 and Silicon oxynitride. The Hafnium-based family of dielectricsincludes hafnium oxide and hafnium silicate/hafnium silicon oxynitride.Hafnium oxide, HfO2, has a dielectric constant twice as much as that ofhafnium silicate/hafnium silicon oxynitride (HfSiO/HfSiON k˜15). Thechoice of the metal is critical for the device to perform properly. Ametal replacing N+ poly as the gate electrode needs to have a workfunction of approximately 4.2 eV for the device to operate properly andat the right threshold voltage. Alternatively, a metal replacing P+ polyas the gate electrode needs to have a work function of approximately 5.2eV to operate properly. The TiAl and TiAlN based family of metals, forexample, could be used to tune the work function of the metal from 4.2eV to 5.2 eV.

FIG. 22F illustrates the structure following deposition, mask, and etchof metal gate 22F02. Optionally, to improve transistor performance, atargeted stress layer to induce a higher channel strain may be employed.A tensile nitride layer may be deposited at low temperature to increasechannel stress for the NMOS devices illustrated in FIG. 22. A PMOStransistor may be constructed via the above process flow by changing theinitial P− wafer or epi-formed P− on N+ layer 2104 to an N− wafer or anN− on P+ epi layer; and the N+ layer 2104 to a P+ layer. Then acompressively stressed nitride film would be deposited post metal gateformation to improve the PMOS transistor performance.

Finally a thick oxide 22G02 may be deposited and contact openings may bemasked and etched preparing the transistors to be connected asillustrated in FIG. 22G. This thick or any low-temperature oxide in thisdocument may be deposited via Chemical Vapor Deposition (CVD), PhysicalVapor Deposition (PVD), or Plasma Enhanced Chemical Vapor Deposition(PECVD) techniques. This flow enables the formation of mono-crystallinetop MOS transistors that could be connected to the underlyingmulti-metal layer semiconductor device without exposing the underlyingdevices and interconnects metals to high temperature. These transistorscould be used as programming transistors of the Antifuse on layer 807,coupled to the pre-processed wafer or layer 808 to create a monolithic3D circuit stack, or for other functions in a 3D integrated circuit.These transistors can be considered “planar transistors,” meaning thatcurrent flow in the transistor channel is substantially in thehorizontal direction. These transistors, as well as others in thisdocument, can also be referred to as horizontal transistors,horizontally oriented transistors, or lateral transistors. Additionally,the gates of transistors in this present invention that include gates on2 or more sides of the transistor channel may be referred to as sidegates. An additional advantage of this flow is that the SmartCut H+, orother atomic species, implant step is done prior to the formation of theMOS transistor gates avoiding potential damage to the gate function. Ifneeded the top layer of the pre-processed wafer or layer 808 couldcomprise a ‘back-gate’ 22F02-1 whereby gate 22F02 may be aligned to bedirectly on top of the back-gate 22F02-1 as illustrated in FIG. 22H. Theback gate 22F02-1 may be formed from the top metal layer in thepre-processed wafer or layer 808 and may utilize the oxide layerdeposited on top of the metal layer for the wafer bonding (not shown) toact as a gate oxide for the back gate.

According to some embodiments of the present invention, during a normalfabrication of the device layers as illustrated in FIG. 8, every newlayer is aligned to the underlying layers using prior alignment marks.Sometimes the alignment marks of one layer could be used for thealignment of multiple layers on top of it and sometimes the new layerwill also have alignment marks to be used for the alignment ofadditional layers put on top of it in the following fabrication step. Solayers of 804 are aligned to layers of 802, layers of 806 are aligned tolayers of 804 and so forth. An advantage of the described process flowis that the layer transferred is thin enough so that during thefollowing patterning step as described in connection to FIG. 22B, thetransferred layer may be aligned to the alignment marks of thepre-processed wafer or layer 808 or those of underneath layers such aslayers 806, 804, 802, or other layers, to form the 3D IC. Therefore the‘back-gate’ 22F02-1 which is part of the top metal layer of thepre-processed wafer or layer 808 would be precisely underneath gate22F02 as all the layers are patterned as being aligned to each other. Inthis context alignment precision may be highly dependent on theequipment used for the patterning steps. For processes of 45 nm andbelow, overlay alignment of better than 5 nm is usually needed. Thealignment requirement only gets tighter with scaling where modernsteppers now can do better than 2 nm. This alignment requirement isorders of magnitude better than what could be achieved for TSV based 3DIC systems as described below in relation to FIG. 12 where even 0.5micron overlay alignment is extremely hard to achieve. Connectionbetween top-gate and back-gate would be made through a top layer via, orTLV. This may allow further reduction of leakage as both the gate 22F02and the back-gate 22F02-1 could be connected together to better shut offthe transistor 22G20. As well, one could create a sleep mode, a normalspeed mode, and fast speed mode by dynamically changing the thresholdvoltage of the top gated transistor by independently changing the biasof the ‘back-gate’ 22F02-1. Additionally, an accumulation mode (fullydepleted) MOSFET transistor could be constructed via the above processflow by changing the initial P-wafer 2102 or epi-formed P− 2106 on N+layer 2104 to an N− wafer or an N− epi layer on N+.

An additional aspect of this technique for forming top transistors isthe size of the via, or TLV, used to connect the top transistors 22G20to the metal layers in pre-processed wafer and layer 808 underneath. Thegeneral rule of thumb is that the size of a via should be larger thanone tenth the thickness of the layer that the via is going through.Since the thickness of the layers in the structures presented in FIG. 12is usually more than 50 micron, the TSV used in such structures areabout 10 micron on the side. The thickness of the transferred layer inFIG. 22A is less than 100 nm and accordingly the vias to connect toptransistors 22G20 to the metal layers in pre-processed wafer and layer808 underneath could be less than 50 nm on the side. As the process isscaled to smaller feature sizes, the thickness of the transferred layerand accordingly the size of the via to connect to the underlyingstructures could be scaled down. For some advanced processes, the endthickness of the transferred layer could be made below 10 nm.

Another alternative for forming the planar top transistors with sourceand drain extensions is to process the prepared wafer of FIG. 21B asshown in FIGS. 29A-29G. FIG. 29A illustrates the layer transferred ontop of pre-processed wafer or layer 808 after the smart cut wherein theN+ 2104 is on top, the P− 2106, and P+ 2108. The oxide layers used tofacilitate the wafer to wafer bond are not shown. Then the substrate P+source 29B04 contact opening and transistor isolation 29B02 is maskedand etched as shown in FIG. 29B. Utilizing an additional masking layer,the isolation region 29C02 is defined by etch all the way to the top ofthe pre-processed wafer or layer 808 to provide full isolation betweentransistors or groups of transistors in FIG. 29C. Etching away the P+layer between transistors is helpful as the P+ layer is conducting. Thena Low-Temperature Oxide 29C04 is deposited and chemically mechanicallypolished. Then a thin polish stop layer 29C06 such as low temperaturesilicon nitride is deposited resulting in the structure illustrated inFIG. 29C. Source 29D02, drain 29D04 and self-aligned Gate 29D06 may bedefined by masking and etching the thin polish stop layer 29C06 and thena sloped N+ etch as illustrated in FIG. 29D. The sloped (30-90 degrees,45 is shown) etch or etches may be accomplished with wet chemistry orplasma etching techniques. This process forms angular source and drainextensions 29D08. FIG. 29E illustrates the structure followingdeposition and densification of a low temperature based Gate Dielectric29E02, or alternatively a low temperature microwave plasma oxidation ofthe silicon surfaces, or an atomic layer deposited (ALD) gatedielectric, to serve as the MOSFET gate oxide, and then deposition of agate material 29E04, such as aluminum or tungsten.

Alternatively, a high-k metal gate structure may be formed as follows.Following an industry standard HF/SC1/SC2 cleaning to create anatomically smooth surface, a high-k dielectric 29E02 is deposited. Thesemiconductor industry has chosen Hafnium-based dielectrics as theleading material of choice to replace SiO₂ and Silicon oxynitride. TheHafnium-based family of dielectrics includes hafnium oxide and hafniumsilicate/hafnium silicon oxynitride. Hafnium oxide, HfO₂, has adielectric constant twice as much as that of hafnium silicate/hafniumsilicon oxynitride (HfSiO/HfSiON k˜15). The choice of the metal iscritical for the device to perform properly. A metal replacing N⁺ polyas the gate electrode needs to have a work function of approximately 4.2eV for the device to operate properly and at the right thresholdvoltage. Alternatively, a metal replacing P⁺ poly as the gate electrodeneeds to have a work function of approximately 5.2 eV to operateproperly. The TiAl and TiAlN based family of metals, for example, couldbe used to tune the work function of the metal from 4.2 eV to 5.2 eV.

FIG. 29F illustrates the structure following a chemical mechanicalpolishing of the metal gate 29E04 utilizing the nitride polish stoplayer 29C06. A PMOS transistor could be constructed via the aboveprocess flow by changing the initial P− wafer or epi-formed P− on N+layer 2104 to an N− wafer or an N− on P+ epi layer; and the N+ layer2104 to a P+ layer. Similarly, layer 2108 would change from P+ to N+ ifthe substrate contact option was used.

Finally a thick oxide 29G02 is deposited and contact openings are maskedand etched preparing the transistors to be connected as illustrated inFIG. 29G. This figure also illustrates the layer transfer silicon via29G04 masked and etched to provide interconnection of the top transistorwiring to the lower layer 808 interconnect wiring 29G06. This flowenables the formation of mono-crystalline top MOS transistors that maybe connected to the underlying multi-metal layer semiconductor devicewithout exposing the underlying devices and interconnects metals to hightemperature. These transistors may be used as programming transistors ofthe antifuse on layer 807, to couple with the pre-processed wafer orlayer 808 to form monolithic 3D ICs, or for other functions in a 3Dintegrated circuit. These transistors can be considered to be “planarMOSFET transistors”, where current flow in the transistor channel is inthe horizontal direction. These transistors can also be referred to ashorizontal transistors or lateral transistors. An additional advantageof this flow is that the SmartCut H+, or other atomic species, implantstep is done prior to the formation of the MOS transistor gates avoidingpotential damage to the gate function. Additionally, an accumulationmode (fully depleted) MOSFET transistor may be constructed via the aboveprocess flow by changing the initial P− wafer or epi-formed P− on N+layer 2104 to an N− wafer or an N− epi layer on N+. Additionally, a backgate similar to that shown in FIG. 22H may be utilized.

Another alternative method is to preprocess the wafer used for layertransfer as illustrated in FIG. 23. FIG. 23A is a drawing illustrationof a pre-processed wafer used for a layer transfer. An N− wafer 2302 isprocessed to have a “buried” layer of N+ 2304, by implant andactivation, or by shallow N+ implant and diffusion followed by an N− epigrowth (epitaxial growth). FIG. 23B is a drawing illustration of thepre-processed wafer made ready for a layer transfer by a deposition orgrowth of an oxide 2308 and by an implant of an atomic species, such asH+, preparing the SmartCut cleaving plane 2306 in the lower part of theN+ region. Now a layer-transfer-flow should be performed to transfer thepre-processed mono-crystalline N− silicon with N+ layer, on top of thepre-processed wafer or layer 808.

FIGS. 24A-24F are drawing illustrations of the formation of planarJunction Gate Field Effect Transistor (JFET) top transistors. FIG. 24Aillustrates the structure after the layer is transferred on top of thepre-processed wafer or layer 808. So, after the smart cut, the N+ 2304is on top and now marked as 24A04. Then the top transistor source 24B04and drain 24B06 are defined by etching away the N+ from the regiondesignated for gates 24B02 and the isolation region between transistors24B08. This step is aligned to the pre-processed wafer or layer 808 sothe formed transistors could be properly connected to the underlyinglayers of pre-processed wafer or layer 808. Then an additional maskingand etch step is performed to remove the N− layer between transistors,shown as 24C02, thus providing better transistor isolation asillustrated in FIG. 24C. FIG. 24D illustrates an optional formation ofshallow P+ region 24D02 for the JFET gate formation. In this optionthere might be a need for laser or other method of optical annealing toactivate the P+. FIG. 24E illustrates how to utilize the laser annealand minimize the heat transfer to pre-processed wafer or layer 808.After the thick oxide deposition 24E02, a layer of Aluminum 24D04, orother light reflecting material, is applied as a reflective layer. Anopening 24D08 in the reflective layer is masked and etched, allowing thelaser light 24D06 to heat the P+ 24D02 implanted area, and reflectingthe majority of the laser energy 24D06 away from pre-processed wafer orlayer 808. Normally, the open area 24D08 is less than 10% of the totalwafer area. Additionally, a copper layer 24D10, or, alternatively, areflective Aluminum layer or other reflective material, may be formed inthe pre-processed wafer or layer 808 that will additionally reflect anyof the unwanted laser energy 24D06 that might travel to pre-processedwafer or layer 808. Layer 24D10 could also be utilized as a ground planeor backgate electrically when the formed devices and circuits are inoperation. Certainly, openings in layer 24D10 would be made throughwhich later thru vias connecting the second top transferred layer to thepre-processed wafer or layer 808 may be constructed. This samereflective laser anneal or other methods of optical anneal techniquemight be utilized on any of the other illustrated structures to enableimplant activation for transistor gates in the second layer transferprocess flow. In addition, absorptive materials may, alone or incombination with reflective materials, also be utilized in the abovelaser or other method of optical annealing techniques. As shown in FIG.24E-1, a photonic energy absorbing layer 24E04, such as amorphouscarbon, may be deposited or sputtered at low temperature over the areathat needs to be laser heated, and then masked and etched asappropriate. This allows the minimum laser or other optical energy to beemployed to effectively heat the area to be implant activated, andthereby minimizes the heat stress on the reflective layers 24D04 & 24D10and the base layer of pre-processed wafer or layer 808. The laserannealing could be done to cover the complete wafer surface or bedirected to the specific regions where the gates are to further reducethe overall heat and further guarantee that no damage, such as thermaldamage, has been caused to the underlying layers, which may includemetals such as, for example, copper or aluminum.

FIG. 24F illustrates the structure, following etching away of the laserreflecting layer 24D04, and the deposition, masking, and etch of a thickoxide 24F04 to open contacts 24F06 and 24F02, and deposition and partialetch-back (or Chemical Mechanical Polishing (CMP)) of aluminum (or othermetal to obtain an optimal Schottky or ohmic contact at 24F02) to formcontacts 24F06 and gate 24F02. If necessary, N+ contacts 24F06 and gatecontact 24F02 can be masked and etched separately to allow a differentmetal to be deposited in each to create a Schottky or ohmic contact inthe gate 24F02 and ohmic connections in the N+ contacts 24F06. The thickoxide 24F04 is a non conducting dielectric material also filling theetched space 24B08 and 24B09 between the top transistors and couldcomprise other isolating material such as silicon nitride. The toptransistors will therefore end up being surrounded by isolatingdielectric unlike conventional bulk integrated circuits transistors thatare built in single crystal silicon wafer and only get covered by nonconducting isolating material. This flow enables the formation ofmono-crystalline top JFET transistors that could be connected to theunderlying multi-metal layer semiconductor device without exposing theunderlying device to high temperature.

Another variation of the previous flow could be in utilizing atransistor technology called pseudo-MOSFET utilizing a molecularmonolayer that is covalently grafted onto the channel region between thedrain and source. This is a process that can be done at relatively lowtemperatures (less than 400° C.).

Another variation is to preprocess the wafer used for layer transfer asillustrated in FIG. 25. FIG. 25A is a drawing illustration of apre-processed wafer used for a layer transfer. An N− wafer 2502 isprocessed to have a “buried” layer of N+ 2504, by implant andactivation, or by shallow N+ implant and diffusion followed by an N− epigrowth (epitaxial growth) 2508. An additional P+ layer 2510 is processedon top. This P+ layer 2510 could again be processed, by implant andactivation, or by P+ epi growth. FIG. 25B is a drawing illustration ofthe pre-processed wafer made ready for a layer transfer by a depositionor growth of an oxide 2512 and by an implant of an atomic species, suchas H+, preparing the SmartCut cleaving plane 2506 in the lower part ofthe N+ 2504 region. Now a layer-transfer-flow should be performed totransfer the pre-processed single crystal silicon with N+ and N− layers,on top of the pre-processed wafer or layer 808.

FIGS. 26A-26E are drawing illustrations of the formation of top planarJFET transistors with back bias or double gate. FIG. 26A illustrates thelayer transferred on top of the pre-processed wafer or layer 808 afterthe smart cut wherein the N+ 2504 is on top. Then the top transistorsource 26B04 and drain 26B06 are defined by etching away the N+ from theregion designated for gates 26B02 and the isolation region betweentransistors 26B08. This step is aligned to the pre-processed wafer orlayer 808 so that the formed transistors could be properly connected tothe underlying layers of pre-processed wafer or layer 808. Then amasking and etch step is performed to remove the N− between transistors26C12 and to allow contact to the now buried P+ layer 2510. And then amasking and etch step is performed to remove in between transistors26C09 the buried P+ layer 2510 for full isolation as illustrated in FIG.26C. FIG. 26D illustrates an optional formation of a shallow P+ region26D02 for gate formation. In this option there might be a need for laseranneal to activate the P+. FIG. 26E illustrates the structure, followingdeposition and etch or CMP of a thick oxide 26E04, and deposition andpartial etch-back of aluminum (or other metal to obtain an optimalSchottky or ohmic contact at 26E02) contacts 26E06, 26E12 and gate26E02. If necessary, N+ contacts 26E06 and gate contact 26E02 can bemasked and etched separately to allow a different metal to be depositedin each to create a Schottky or ohmic contact in the gate 26E02 andSchottky or ohmic connections in the N+ contacts 26E06 & 26E12. Thethick oxide 26E04 is a non conducting dielectric material also fillingthe etched space 26B08 and 26C09 between the top transistors and couldbe comprised from other isolating material such as silicon nitride.Contact 26E12 is to allow a back bias of the transistor or can beconnected to the gate 26E02 to provide a double gate JFET. Alternativelythe connection for back bias could be included in layers of thepre-processed wafer or layer 808 connecting to layer 2510 fromunderneath. This flow enables the formation of mono-crystalline topultra thin body planar JFET transistors with back bias or double gatecapabilities that may be connected to the underlying multi-metal layersemiconductor device without exposing the underlying device to hightemperature.

Another alternative is to preprocess the wafer used for layer transferas illustrated in FIG. 27. FIG. 27A is a drawing illustration of apre-processed wafer used for a layer transfer. An N+ wafer 2702 isprocessed to have “buried” layers either by ion implantation andactivation anneals, or by diffusion to create a vertical structure to bethe building block for NPN (or PNP) bipolar junction transistors. Multilayer epitaxial growth of the layers may also be utilized to create thedoping layered structure. Starting with P layer 2704, then N− layer2708, and finally N+ layer 2710 and then activating these layers byheating to a high activation temperature. FIG. 27B is a drawingillustration of the pre-processed wafer made ready for a layer transferby a deposition or growth of an oxide 2712 and by an implant of anatomic species, such as H+, preparing the SmartCut cleaving plane 2706in the N+ region. Now a layer-transfer-flow should be performed totransfer the pre-processed layers, on top of pre-processed wafer orlayer 808.

FIGS. 28A-28E are drawing illustrations of the formation of top layerbipolar junction transistors. FIG. 28A illustrates the layer transferredon top of wafer or layer 808 after the smart cut wherein the N+ 28A02which was part of 2702 is now on top. Effectively at this point there isa giant transistor overlaying the entire wafer. The following steps aremultiple etch steps as illustrated in FIG. 28B to 28D where the gianttransistor is cut and defined as needed and aligned to the underlyinglayers of pre-processed wafer or layer 808. These etch steps also exposethe different layers comprising the bipolar transistors to allowcontacts to be made with the emitter 2806, base 2802 and collector 2808,and etching all the way to the top oxide of pre-processed wafer or layer808 to isolate between transistors as 2809 in FIG. 28D. The top N+ dopedlayer 28A02 may be masked and etched as illustrated in FIG. 28B to formthe emitter 2806. Then the p 2704 and N− 2706 doped layers may be maskedand etched as illustrated in FIG. 28C to form the base 2802. Then thecollector layer 2710 may be masked and etched to the top oxide ofpre-processed wafer or layer 808, thereby creating isolation 2809between transistors as illustrated in FIG. 28D. Then the entirestructure may be covered with a Low Temperature Oxide 2804, the oxideplanarized with CMP, and then masked and etched to form contacts to theemitter 2806, base 2802 and collector 2808 as illustrated in FIG. 28E.The oxide 2804 is a non conducting dielectric material also filling theetched space 2809 between the top transistors and could be comprisedfrom other isolating material such as silicon nitride. This flow enablesthe formation of mono-crystalline top bipolar transistors that could beconnected to the underlying multi-metal layer semiconductor devicewithout exposing the underlying device to high temperature.

The bipolar transistors formed with reference to FIGS. 27 and 28 may beused to form analog or digital BiCMOS circuits where the CMOStransistors are on the substrate primary layer 802 with pre-processedwafer or layer 808 and the bipolar transistors may be formed in thetransferred top layer.

Another class of devices that may be constructed partly at hightemperature before layer transfer to a substrate with metalinterconnects and then completed at low temperature after layer transferis a junction-less transistor (JLT). For example, in deep sub-micronprocesses copper metallization is utilized, so a high temperature wouldbe above approximately 400° C., whereby a low temperature would beapproximately 400° C. and below. The junction-less transistor structureavoids the sharply graded junctions needed as silicon technology scales,and provides the ability to have a thicker gate oxide for an equivalentperformance when compared to a traditional MOSFET transistor. Thejunction-less transistor is also known as a nanowire transistor withoutjunctions, or gated resistor, or nanowire transistor as described in apaper by Jean-Pierre Colinge, et. al., published in NatureNanotechnology on Feb. 21, 2010. The junction-less transistors may beconstructed whereby the transistor channel is a thin solid piece ofevenly and heavily doped single crystal silicon. The dopingconcentration of the channel may be identical to that of the source anddrain. The considerations may include the nanowire channel must be thinand narrow enough to allow for full depletion of the carriers when thedevice is turned off, and the channel doping must be high enough toallow a reasonable current to flow when the device is on. Theseconsiderations may lead to tight process variation boundaries forchannel thickness, width, and doping for a reasonably obtainable gatework function and gate oxide thickness.

One of the challenges of a junction-less transistor device is turningthe channel off with minimal leakage at a zero gate bias. To enhancegate control over the transistor channel, the channel may be dopedunevenly; whereby the heaviest doping is closest to the gate or gatesand the channel doping is lighter the farther away from the gateelectrode. One example would be where the center of a 2, 3, or 4 gatesided junction-less transistor channel is more lightly doped than theedges. This may enable much lower off currents for the same gate workfunction and control. FIGS. 52 A and 52B show, on logarithmic and linearscales respectively, simulated drain to source current Ids as a functionof the gate voltage Vg for various junction-less transistor channeldopings where the total thickness of the n-channel is 20 nm. Two of thefour curves in each figure correspond to evenly doping the 20 nm channelthickness to 1E17 and 1E18 atoms/cm3, respectively. The remaining twocurves show simulation results where the 20 nm channel has two layers of10 nm thickness each. In the legend denotations for the remaining twocurves, the first number corresponds to the 10 nm portion of the channelthat is the closest to the gate electrode. For example, the curveD=1E18/1E17 shows the simulated results where the 10 nm channel portiondoped at 1E18 is closest to the gate electrode while the nm channelportion doped at 1E17 is farthest away from the gate electrode. In FIG.52 A, curves 5202 and 5204 correspond to doping patterns of D=1E18/1E17and D=1E17/1E18, respectively. According to FIG. 52A, at a Vg of 0volts, the off current for the doping pattern of D=1E18/1E17 isapproximately 50 times lower than that of the reversed doping pattern ofD=1E17/1E18. Likewise, in FIG. 52 B, curves 5206 and 5208 correspond todoping patterns of D=1E18/1E17 and D=1E17/1E18, respectively. FIG. 52Bshows that at a Vg of 1 volt, the Ids of both doping patterns are withina few percent of each other.

The junction-less transistor channel may be constructed with even,graded, or discrete layers of doping. The channel may be constructedwith materials other than doped mono-crystalline silicon, such aspoly-crystalline silicon, or other semi-conducting, insulating, orconducting material, such as graphene or other graphitic material, andmay be in combination with other layers of similar or differentmaterial. For example, the center of the channel may comprise a layer ofoxide, or of lightly doped silicon, and the edges more heavily dopedsingle crystal silicon. This may enhance the gate control effectivenessfor the off state of the resistor, and may also increase the on-currentdue to strain effects on the other layer or layers in the channel.Strain techniques may also be employed from covering and insulatormaterial above, below, and surrounding the transistor channel and gate.Lattice modifiers may also be employed to strain the silicon, such as anembedded SiGe implantation and anneal. The cross section of thetransistor channel may be rectangular, circular, or oval shaped, toenhance the gate control of the channel. Alternatively, to optimize themobility of the P-channel junction-less transistor in the 3D layertransfer method, the donor wafer may be rotated 90 degrees with respectto the acceptor wafer prior to bonding to facilitate the creation of theP-channel in the <110> silicon plane direction.

To construct an n-type 4-sided gated junction-less transistor a siliconwafer is preprocessed to be used for layer transfer as illustrated inFIG. 56A-56G. These processes may be at temperatures above 400 degreeCentigrade as the layer transfer to the processed substrate with metalinterconnects has yet to be done. As illustrated in FIG. 56A, an N−wafer 5600A is processed to have a layer of N+ 5604A, by implant andactivation, by an N+ epitaxial growth, or may be a deposited layer ofheavily N+ doped polysilicon. A gate oxide 5602A may be grown before orafter the implant, to a thickness approximately half of the finaltop-gate oxide thickness. FIG. 56B is a drawing illustration of thepre-processed wafer made ready for a layer transfer by an implant 5606of an atomic species, such as H+, preparing the “cleaving plane” 5608 inthe N− region 5600A of the substrate and plasma or other surfacetreatments to prepare the oxide surface for wafer oxide to oxidebonding. Another wafer is prepared as above without the H+ implant andthe two are bonded as illustrated in FIG. 56C, to transfer thepre-processed single crystal N− silicon with N+ layer and half gateoxide, on top of a similarly pre-processed, but not cleave implanted, N−wafer 5600 with N+ layer 5604 and oxide 5602. The top wafer is cleavedand removed from the bottom wafer. This top wafer may now also beprocessed and reused for more layer transfers to form the resistorlayer. The remaining top wafer N− and N+ layers are chemically andmechanically polished to a very thin N+ silicon layer 5610 asillustrated in FIG. 56D. This thin N+ doped silicon layer 5610 is on theorder of 5 to 40 nm thick and will eventually form the resistor thatwill be gated on four sides. The two ‘half’ gate oxides 5602, 5602A maynow be atomically bonded together to form the gate oxide 5612, whichwill eventually become the top gate oxide of the junction-lesstransistor in FIG. 56E. A high temperature anneal may be performed toremove any residual oxide or interface charges.

Alternatively, the wafer that becomes the bottom wafer in FIG. 56C maybe constructed wherein the N+ layer 5604 may be formed with heavilydoped polysilicon and the half gate oxide 5602 is deposited or grownprior to layer transfer. The bottom wafer N+ silicon or polysiliconlayer 5604 will eventually become the top-gate of the junction-lesstransistor.

As illustrated in FIGS. 56E to 56G, the wafer is conventionallyprocessed, at temperatures higher than 400° C. as necessary, inpreparation to layer transfer the junction-less transistor structure tothe processed ‘house’ wafer 808. A thin oxide may be grown to protectthe thin resistor silicon 5610 layer top, and then parallel wires 5614of repeated pitch of the thin resistor layer may be masked and etched asillustrated in FIG. 56E and then the photoresist is removed. The thinoxide, if present, may be striped in a dilute hydrofluoric acid (HF)solution and a conventional gate oxide 5616 is grown and polysilicon5618, doped or undoped, is deposited as illustrated in FIG. 56F. Thepolysilicon is chemically and mechanically polished (CMP'ed) flat and athin oxide 5620 is grown or deposited to facilitate a low temperatureoxide to oxide wafer bonding in the next step. The polysilicon 5618 maybe implanted for additional doping either before or after the CMP. Thispolysilicon will eventually become the bottom and side gates of thejunction-less transistor. FIG. 56G is a drawing illustration of thewafer being made ready for a layer transfer by an implant 5606 of anatomic species, such as H+, preparing the “cleaving plane” 5608G in theN− region 5600 of the substrate and plasma or other surface treatmentsto prepare the oxide surface for wafer oxide to oxide bonding. Theacceptor wafer 808 with logic transistors and metal interconnects isprepared for a low temperature oxide to oxide wafer bond with surfacetreatments of the top oxide and the two are bonded as illustrated inFIG. 56H. The top donor wafer is cleaved and removed from the bottomacceptor wafer 808 and the top N− substrate is removed by CMP (chemicalmechanical polish). A metal interconnect strip 5622 in the house 808 isalso illustrated in FIG. 56H.

FIG. 56I is a top view of a wafer at the same step as FIG. 56H with twocross-sectional views I and II. The N+ layer 5604, which will eventuallyform the top gate of the resistor, and the top gate oxide 5612 will gateone side of the resistor line 5614, and the bottom and side gate oxide5616 with the polysilicon bottom and side gates 5618 will gate the otherthree sides of the resistor 5614. The logic house wafer 808 has a topoxide layer 5624 that also encases the top metal interconnect strip5622, extent shown as dotted lines in the top view.

In FIG. 56J, a polish stop layer 5626 of a material such as oxide andsilicon nitride is deposited on the top surface of the wafer, andisolation openings 5628 are masked and etched to the depth of the house808 oxide 5624 to fully isolate transistors. The isolation openings 5628are filled with a low temperature gap fill oxide, and chemically andmechanically polished (CMP'ed) flat. The top gate 5630 is masked andetched as illustrated in FIG. 56K, and then the etched openings 5629 arefilled with a low temperature gap fill oxide deposition, and chemicallyand mechanically (CMP'ed) polished flat, then an additional oxide layeris deposited to enable interconnect metal isolation.

The contacts are masked and etched as illustrated in FIG. 56L. The gatecontact 5632 is masked and etched, so that the contact etches throughthe top gate layer 5630, and during the metal opening mask and etchprocess the gate oxide is etched and the top 5630 and bottom 5618 gatesare connected together. The contacts 5634 to the two terminals of theresistor layer 5614 are masked and etched. And then the thru vias 5636to the house wafer 808 and metal interconnect strip 5622 are masked andetched.

As illustrated in FIG. 56M, the metal lines 5640 are mask defined andetched, filled with barrier metals and copper interconnect, and CMP'edin a normal metal interconnect scheme, thereby completing the contactvia 5632 simultaneous coupling to the top 5630 and bottom 5618 gates,the two terminals 5634 of the resistor layer 5614, and the thru via tothe house wafer 808 metal interconnect strip 5622. This flow enables theformation of a mono-crystalline 4-sided gated junction-less transistorthat could be connected to the underlying multi-metal layersemiconductor device without exposing the underlying devices to hightemperature.

Alternatively, as illustrated in FIGS. 96A to 96J, an n-channel 4-sidedgated junction-less transistor (JLT) may be constructed that is suitablefor 3D IC manufacturing. 4-sided gated JLTs can also be referred to asgate-all around JLTs or silicon nano-wire JLTs.

As illustrated in FIG. 96A, a P− (shown) or N− substrate donor wafer9600 may be processed to comprise wafer sized layers of N+ doped silicon9602 and 9606, and wafer sized layers of n+ SiGe 9604 and 9608. Layers9602, 9604, 9606, and 9608 may be grown epitaxially and are carefullyengineered in terms of thickness and stoichiometry to keep the defectdensity due to the lattice mismatch between Si and SiGe low. Thestoichiometry of the SiGe may be unique to each SiGe layer to providefor different etch rates as will be described later. Some techniques forachieving this include keeping the thickness of the SiGe layers belowthe critical thickness for forming defects. The top surface of donorwafer 9600 may be prepared for oxide wafer bonding with a deposition ofan oxide 9613. These processes may be done at temperatures aboveapproximately 400° C. as the layer transfer to the processed substratewith metal interconnects has yet to be done. A wafer sized layer denotesa continuous layer of material or combination of materials that extendsacross the wafer to the full extent of the wafer edges and may beapproximately uniform in thickness. If the wafer sized layer compromisesdopants, then the dopant concentration may be substantially the same inthe x and y direction across the wafer, but can vary in the z directionperpendicular to the wafer surface.

As illustrated in FIG. 96B, a layer transfer demarcation plane 9699(shown as a dashed line) may be formed in donor wafer 9600 by hydrogenimplantation or other methods as previously described.

As illustrated in FIG. 96C, both the donor wafer 9600 and acceptor wafer9610 top layers and surfaces may be prepared for wafer bonding aspreviously described and then donor wafer 9600 is flipped over, alignedto the acceptor wafer 9610 alignment marks (not shown) and bondedtogether at a low temperature (less than approximately 400° C.). Oxide9613 from the donor wafer and the oxide of the surface of the acceptorwafer 9610 are thus atomically bonded together are designated as oxide9614.

As illustrated in FIG. 96D, the portion of the P− donor wafer substrate9600 that is above the layer transfer demarcation plane 9699 may beremoved by cleaving and polishing, etching, or other low temperatureprocesses as previously described. A CMP process may be used to removethe remaining P− layer until the N+ silicon layer 9602 is reached. Thisprocess of an ion implanted atomic species, such as Hydrogen, forming alayer transfer demarcation plane, and subsequent cleaving or thinning,may be called ‘ion-cut’. Acceptor wafer 9610 may have similar meaningsas wafer 808 previously described with reference to FIG. 8.

As illustrated in FIG. 96E, stacks of N+ silicon and n+ SiGe regionsthat will become transistor channels and gate areas may be formed bylithographic definition and plasma/RIE etching of N+ silicon layers 9602& 9606 and n+ SiGe layers 9604 & 9608. The result is stacks of n+ SiGe9616 and N+ silicon 9618 regions. The isolation between stacks may befilled with a low temperature gap fill oxide 9620 and chemically andmechanically polished (CMP'ed) flat. This will fully isolate thetransistors from each other. The stack ends are exposed in theillustration for clarity of understanding.

As illustrated in FIG. 96F, eventual ganged or common gate area 9630 maybe lithographically defined and oxide etched. This will expose thetransistor channels and gate area stack sidewalls of alternating N+silicon 9618 and n+ SiGe 9616 regions to the eventual ganged or commongate area 9630. The stack ends are exposed in the illustration forclarity of understanding.

As illustrated in FIG. 96G, the exposed n+ SiGe regions 9616 may beremoved by a selective etch recipe that does not attack the N+ siliconregions 9618. This creates air gaps between the N+ silicon regions 9618in the eventual ganged or common gate area 9630. Such etching recipesare described in “High performance 5 nm radius twin silicon nanowireMOSFET (TSNWFET): Fabrication on bulk Si wafer, characteristics, andreliability,” in Proc. IEDM Tech. Dig., 2005, pp. 717-720 by S. D. Suk,et. al. The n+ SiGe layers farthest from the top edge may bestoichiometrically crafted such that the etch rate of the layer (nowregion) farthest from the top (such as n+ SiGe layer 9608) may etchslightly faster than the layer (now region) closer to the top (such asn+ SiGe layer 9604), thereby equalizing the eventual gate lengths of thetwo stacked transistors. The stack ends are exposed in the illustrationfor clarity of understanding.

As illustrated in FIG. 96H, an optional step of reducing the surfaceroughness, rounding the edges, and thinning the diameter of the N+silicon regions 9618 that are exposed in the ganged or common gate areamay utilize a low temperature oxidation and subsequent HF etch removalof the oxide just formed. This may be repeated multiple times. Hydrogenmay be added to the oxidation or separately utilized atomically as aplasma treatment to the exposed N+ silicon surfaces. The result may be arounded silicon nanowire-like structure to form the eventual transistorgated channel 9636. The stack ends are exposed in the illustration forclarity of understanding.

As illustrated in FIG. 96I a low temperature based Gate Dielectric maybe deposited and densified to serve as the junction-less transistor gateoxide. Alternatively, a low temperature microwave plasma oxidation ofthe eventual transistor gated channel 9636 silicon surfaces may serve asthe JLT gate oxide or an atomic layer deposition (ALD) technique may beutilized to form the HKMG gate oxide as previously described. Thendeposition of a low temperature gate material 9612, such as P+ dopedamorphous silicon, may be performed. Alternatively, a HKMG gatestructure may be formed as described previously. A CMP is performedafter the gate material deposition. The stack ends are exposed in theillustration for clarity of understanding.

FIG. 96J shows the complete JLT transistor stack formed in FIG. 96I withthe oxide removed for clarity of viewing, and a cross-sectional cut I ofFIG. 96I. Gate 9612 surrounds the transistor gated channel 9636 and eachganged transistor stack is isolated from one another by oxide 9622. Thesource and drain connections of the transistor stacks can be made to theN+ Silicon 9618 and n+ SiGe 9616 regions that are not covered by thegate 9612.

Contacts to the 4-sided gated JLT's source, drain, and gate may be madewith conventional Back end of Line (BEOL) processing as describedpreviously and coupling from the formed JLTs to the acceptor wafer maybe accomplished with formation of a thru layer via (TLV) connection toan acceptor wafer metal interconnect pad. This flow enables theformation of a mono-crystalline silicon channel 4-sided gatedjunction-less transistor that may be formed and connected to theunderlying multi-metal layer semiconductor device without exposing theunderlying devices to a high temperature.

A p channel 4-sided gated JLT may be constructed as above with the N+silicon layers 9602 and 9608 formed as P+ doped, and the gate metals9612 are of appropriate work function to shutoff the p channel at a gatevoltage of zero.

While the process flow shown in FIG. 96A-J illustrates the key stepsinvolved in forming a four-sided gated JLT with 3D stacked components,it is conceivable to one skilled in the art that changes to the processcan be made. For example, process steps and additional materials/regionsto add strain to JLTs may be added. Or N+ SiGe layers 9604 and 9608 mayinstead be comprised of p+ SiGe or undoped SiGe and the selectiveetchant formula adjusted. Furthermore, more than two layers of chips orcircuits can be 3D stacked. Also, there are many methods to constructsilicon nanowire transistors. These are described in “High performanceand highly uniform gate-all-around silicon nanowire MOSFETs with wiresize dependent scaling,” Electron Devices Meeting (IEDM), 2009 IEEEInternational, vol., no., pp. 1-4, 7-9 Dec. 2009 by Bangsaruntip, S.;Cohen, G. M.; Majumdar, A.; et al. (“Bangsaruntip”) and in “Highperformance 5 nm radius twin silicon nanowire MOSFET (TSNWFET):Fabrication on bulk Si wafer, characteristics, and reliability,” inProc. IEDM Tech. Dig., 2005, pp. 717-720 by S. D. Suk, S.-Y. Lee, S.-M.Kim, et al. (“Suk”). Contents of these publications are incorporated inthis document by reference. The techniques described in thesepublications can be utilized for fabricating four-sided gated JLTs.

Alternatively, an n-type 3-sided gated junction-less transistor may beconstructed as illustrated in FIGS. 57 A to 57G. A silicon wafer ispreprocessed to be used for layer transfer as illustrated in FIGS. 57Aand 57B. These processes may be at temperatures above 400° C. as thelayer transfer to the processed substrate with metal interconnects hasyet to be done. As illustrated in FIG. 57A, an N− wafer 5700 isprocessed to have a layer of N+ 5704, by implant and activation, by anN+ epitaxial growth, or may be a deposited layer of heavily N+ dopedpolysilicon. A screen oxide 5702 may be grown before the implant toprotect the silicon from implant contamination and to provide an oxidesurface for later wafer to wafer bonding. FIG. 57B is a drawingillustration of the pre-processed wafer made ready for a layer transferby an implant 5707 of an atomic species, such as H+, preparing the“cleaving plane” 5708 in the N− region 5700 of the donor substrate andplasma or other surface treatments to prepare the oxide surface forwafer oxide to oxide bonding. The acceptor wafer or house 808 with logictransistors and metal interconnects is prepared for a low temperatureoxide to oxide wafer bond with surface treatments of the top oxide andthe two are bonded as illustrated in FIG. 57C. The top donor wafer iscleaved and removed from the bottom acceptor wafer 808 and the top N−substrate is chemically and mechanically polished (CMP'ed) into the N+layer 5704 to form the top gate layer of the junction-less transistor. Ametal interconnect layer 5706 in the acceptor wafer or house 808 is alsoillustrated in FIG. 57C. For illustration simplicity and clarity, thedonor wafer oxide layer 5702 will not be drawn independent of theacceptor wafer or house 808 oxides in FIGS. 57D through 57G.

A thin oxide may be grown to protect the thin transistor silicon 5704layer top, and then the transistor channel elements 5708 are masked andetched as illustrated in FIG. 57D and then the photoresist is removed.The thin oxide is striped in a dilute HF solution and a low temperaturebased Gate Dielectric may be deposited and densified to serve as thejunction-less transistor gate oxide 5710. Alternatively, a lowtemperature microwave plasma oxidation of the silicon surfaces may serveas the junction-less transistor gate oxide 5710 or an atomic layerdeposition (ALD) technique may be utilized.

Then deposition of a low temperature gate material 5712, such as dopedor undoped amorphous silicon as illustrated in FIG. 57E, may beperformed. Alternatively, a high-k metal gate structure may be formed asdescribed previously. The gate material 5712 is then masked and etchedto define the top and side gates 5714 of the transistor channel elements5708 in a crossing manner, generally orthogonally as shown in FIG. 57F.

Then the entire structure may be covered with a Low Temperature Oxide5716, the oxide planarized with chemical mechanical polishing, and thencontacts and metal interconnects may be masked and etched as illustratedFIG. 57G. The gate contact 5720 connects to the gate 5714. The twotransistor channel terminal contacts 5722 independently connect totransistor element 5708 on each side of the gate 5714. The thru via 5724connects the transistor layer metallization to the acceptor wafer orhouse 808 at interconnect 5706. This flow enables the formation ofmono-crystalline 3-sided gated junction-less transistor that may beformed and connected to the underlying multi-metal layer semiconductordevice without exposing the underlying devices to a high temperature.

Alternatively, an n-type 3-sided gated thin-side-up junction-lesstransistor may be constructed as follows in FIGS. 58 A to 58G. Athin-side-up junction-less transistor may have the thinnest dimension ofthe channel cross-section facing up (oriented horizontally), that facebeing parallel to the silicon base substrate surface. Previously andsubsequently described junction-less transistors may have the thinnestdimension of the channel cross section oriented vertically andperpendicular to the silicon base substrate surface. A silicon wafer ispreprocessed to be used for layer transfer, as illustrated in FIGS. 58Aand 58B. These processes may be at temperatures above 400° C. as thelayer transfer to the processed substrate with metal interconnects hasyet to be done. As illustrated in FIG. 58A, an N− wafer 5800 may beprocessed to have a layer of N+ 5804, by ion implantation andactivation, by an N+ epitaxial growth, or may be a deposited layer ofheavily N+ doped polysilicon. A screen oxide 5802 may be grown beforethe implant to protect the silicon from implant contamination and toprovide an oxide surface for later wafer to wafer bonding. FIG. 58B is adrawing illustration of the pre-processed wafer made ready for a layertransfer by an implant 5806 of an atomic species, such as H+, preparingthe “cleaving plane” 5808 in the N− region 5800 of the donor substrate,and plasma or other surface treatments to prepare the oxide surface forwafer oxide to oxide bonding. The acceptor wafer 808 with logictransistors and metal interconnects is prepared for a low temperatureoxide to oxide wafer bond with surface treatments of the top oxide andthe two are bonded as illustrated in FIG. 58C. The top donor wafer iscleaved and removed from the bottom acceptor wafer 808 and the top N−substrate is chemically and mechanically polished (CMP'ed) into the N+layer 5804 to form the junction-less transistor channel layer. FIG. 58Calso illustrates the deposition of a CMP and plasma etch stop layer5805, such as low temperature SiN on oxide, on top of the N+ layer 5804.A metal interconnect layer 5806 in the acceptor wafer or house 808 isalso shown in FIG. 58C. For illustration simplicity and clarity, thedonor wafer oxide layer 5802 will not be drawn independent of theacceptor wafer or house 808 oxide in FIGS. 58D through 58G.

The transistor channel elements 5808 are masked and etched asillustrated in FIG. 58D and then the photoresist is removed. Asillustrated in FIG. 58E, a low temperature based Gate Dielectric may bedeposited and densified to serve as the junction-less transistor gateoxide 5810. Alternatively, a low temperature microwave plasma oxidationof the silicon surfaces may serve as the junction-less transistor gateoxide 5810 or an atomic layer deposition (ALD) technique may beutilized. Then deposition of a low temperature gate material 5812, suchas P+ doped amorphous silicon may be performed. Alternatively, a high-kmetal gate structure may be formed as described previously. The gatematerial 5812 is then masked and etched to define the top and side gates5814 of the transistor channel elements 5808. As illustrated in FIG.58G, the entire structure may be covered with a Low Temperature Oxide5816, the oxide planarized with chemical mechanical polishing (CMP), andthen contacts and metal interconnects may be masked and etched. The gatecontact 5820 connects to the resistor gate 5814 (i.e., in front of andbehind the plane of the other elements shown in FIG. 58G). The twotransistor channel terminal contacts 5822 per transistor independentlyconnect to the transistor channel element 5808 on each side of the gate5814. The thru via 5824 connects the transistor layer metallization tothe acceptor wafer or house 808 interconnect 5806. This flow enables theformation of mono-crystalline 3-gated sided thin-side-up junction-lesstransistor that may be formed and connected to the underlyingmulti-metal layer semiconductor device without exposing the underlyingdevices to a high temperature. Persons of ordinary skill in the art willappreciate that the illustrations in FIGS. 57A through 57G and FIGS. 58Athrough 58G are exemplary only and are not drawn to scale. Such skilledpersons will further appreciate that many variations are possible like,for example, the process described in conjunction with FIGS. 57A through57G could be used to make a junction-less transistor where the channelis taller than its width or that the process described in conjunctionwith FIGS. 58A through 58G could be used to make a junction-lesstransistor that is wider than its height. Many other modificationswithin the scope of the invention will suggest themselves to suchskilled persons after reading this specification. Thus the invention isto be limited only by the appended claims.

Alternatively, a two layer n-type 3-sided gated junction-less transistormay be constructed as shown in FIGS. 61A to 61I. This structure mayimprove the source and drain contact resistance by providing for ahigher doping at the contact surface than the channel. Additionally,this structure may be utilized to create a two layer channel wherein thelayer closest to the gate is more highly doped. A silicon wafer may bepreprocessed for layer transfer as illustrated in FIGS. 61A and 61B.These preprocessings may be performed at temperatures above 400° C. asthe layer transfer to the processed substrate with metal interconnectshas yet to be done. As illustrated in FIG. 61A, an N− wafer 6100 isprocessed to have two layers of N+, the top layer 6104 with a lowerdoping concentration than the bottom N+ layer 6103, by an implant andactivation, or an N+ epitaxial growth, or combinations thereof. One ormore depositions of in-situ doped amorphous silicon may also be utilizedto create the vertical dopant layers or gradients. A screen oxide 6102may be grown before the implant to protect the silicon from implantcontamination and to provide an oxide surface for later wafer-to-waferbonding. FIG. 61B is a drawing illustration of the pre-processed waferfor a layer transfer by an implant 6107 of an atomic species, such asH+, preparing the “cleaving plane” 6109 in the N-region 6100 of thedonor substrate and plasma or other surface treatments to prepare theoxide surface for wafer oxide to oxide bonding.

The acceptor wafer or house 808 with logic transistors and metalinterconnects is prepared for a low temperature oxide-to-oxide waferbond with surface treatments of the top oxide and the two are bonded asillustrated in FIG. 61C. The top donor wafer is cleaved and removed fromthe bottom acceptor wafer 808 and the top N− substrate is chemically andmechanically polished (CMP'ed) into the more highly doped N+ layer 6103.An etch hard mask layer of low temperature silicon nitride 6105 may bedeposited on the surface of 6103, including a thin oxide stress bufferlayer. A metal interconnect metal pad or strip 6106 in the acceptorwafer or house 808 is also illustrated in FIG. 61C. For illustrationsimplicity and clarity, the donor wafer oxide layer 6102 will not bedrawn independent of the acceptor wafer or house 808 oxide in subsequentFIGS. 61D through 61I.

The source and drain connection areas may be masked, the silicon nitride6105 layer may be etched, and the photoresist may be stripped. A partialor full silicon plasma etch may be performed, or a low temperatureoxidation and then Hydrofluoric Acid etch of the oxide may be performed,to thin layer 6103. FIG. 61D illustrates a two-layer channel, asdescribed and simulated above in conjunction with FIGS. 52A and 52B,formed by thinning layer 6103 with the above etch process to almostcomplete removal, leaving some of layer 6103 remaining on top of 6104and the full thickness of 6103 still remaining underneath 6105. Acomplete removal of the top channel layer 6103 may also be performed.This etch process may also be utilized to adjust for wafer-to-wafer CMPvariations of the remaining donor wafer layers, such as 6100 and 6103,after the layer transfer cleave to provide less variability in thechannel thickness.

FIG. 61E illustrates the photoresist 6150 definition of the source 6151(one full thickness 6103 region), drain 6152 (the other full thickness6103 region), and channel 5153 (region of partial 6130 thickness andfull 6104 thickness) of the junction-less transistor.

The exposed silicon remaining on layer 6104, as illustrated in FIG. 61F,may be plasma etched and the photoresist 6150 may be removed. Thisprocess may provide for an isolation between devices and may define thechannel width of the junction-less transistor channel 6108.

A low temperature based Gate Dielectric may be deposited and densifiedto serve as the junction-less transistor gate oxide 6110 as illustratedin FIG. 61G. Alternatively, a low temperature microwave plasma oxidationof the silicon surfaces may provide the junction-less transistor gateoxide 6110 or an atomic layer deposition (ALD) technique may beutilized. Then deposition of a low temperature gate material 6112, suchas, for example, doped amorphous silicon, may be performed, asillustrated in FIG. 61G. Alternatively, a high-k metal gate structuremay be formed as described previously.

The gate material 6112 may then be masked and etched to define the topand side gates 6114 of the transistor channel elements 6108 in acrossing manner, generally orthogonally, as illustrated in FIG. 61H.Then the entire structure may be covered with a Low Temperature Oxide6116, the oxide may be planarized by chemical mechanical polishing.

Then contacts and metal interconnects may be masked and etched asillustrated FIG. 61I. The gate contact 6120 may be connected to the gate6114. The two transistor source/drain terminal contacts 6122 may beindependently connected to the heavier doped layer 6103 and then totransistor channel element 6108 on each side of the gate 6114. The thruvia 6124 may connect the junction-less transistor layer metallization tothe acceptor wafer or house 808 at interconnect pad or strip 6106. Thethru via 6124 may be independently masked and etched to provide processmargin with respect to the other contacts 6122 and 6120. This flow mayenable the formation of mono-crystalline two layer 3-sided gatedjunction-less transistor that may be formed and connected to theunderlying multi-metal layer semiconductor device without exposing theunderlying devices to a high temperature.

Alternatively, a 1-sided gated junction-less transistor can beconstructed as shown in FIG. 65A-C. A thin layer of heavily dopedsilicon 6503 may be transferred on top of the acceptor wafer or house808 using layer transfer techniques described previously wherein thedonor wafer oxide layer 6501 may be utilized to form an oxide to oxidebond with the top of the acceptor wafer or house 808. The transferreddoped layer 6503 may be N+ doped for an n-channel junction-lesstransistor or may be P+ doped for a p-channel junction-less transistor.As illustrated in FIG. 65B, oxide isolation 6506 may be formed bymasking and etching the N+ layer 6503 and subsequent deposition of a lowtemperature oxide which may be chemical mechanically polished to thechannel silicon 6503 thickness. The channel thickness 6503 may also beadjusted at this step. A low temperature gate dielectric 6504 and gatemetal 6505 are deposited or grown as previously described and thenphoto-lithographically defined and etched. As shown in FIG. 65C, a lowtemperature oxide 6508 may then be deposited, which also may provide amechanical stress on the channel for improved carrier mobility. Contactopenings 6510 may then be opened to various terminals of thejunction-less transistor. Persons of ordinary skill in the art willappreciate that the processing methods presented above are illustrativeonly and that other embodiments of the inventive principles describedherein are possible and thus the scope if the invention is only limitedby the appended claims.

A family of vertical devices can also be constructed as top transistorsthat are precisely aligned to the underlying pre-fabricated acceptorwafer or house 808. These vertical devices have implanted and annealedsingle crystal silicon layers in the transistor by utilizing the“SmartCut” layer transfer process that does not exceed the temperaturelimit of the underlying pre-fabricated structure. For example, verticalstyle MOSFET transistors, floating gate flash transistors, floating bodyDRAM, thyristor, bipolar, and Schottky gated JFET transistors, as wellas memory devices, can be constructed. Junction-less transistors mayalso be constructed in a similar manner. The gates of the verticaltransistors or resistors may be controlled by memory or logic elementssuch as MOSFET, DRAM, SRAM, floating flash, anti-fuse, floating bodydevices, etc. that are in layers above or below the vertical device, orin the same layer. As an example, a vertical gate-all-around n-MOSFETtransistor construction is described below.

The donor wafer preprocessed for the general layer transfer process isillustrated in FIG. 39. A P− wafer 3902 is processed to have a “buried”layer of N+ 3904, by either implant and activation, or by shallow N+implant and diffusion. This process may be followed by depositing an P−epi growth (epitaxial growth) layer 3906 and finally an additional N+layer 3908 may be processed on top. This N+ layer 2510 could again beprocessed, by implant and activation, or by N+ epi growth.

FIG. 39B is a drawing illustration of the pre-processed wafer made readyfor a conductive bond layer transfer by a deposition of a conductivebarrier layer 3910 such as TiN or TaN on top of N+ layer 3908 and animplant of an atomic species, such as H+, preparing the SmartCutcleaving plane 3912 in the lower part of the N+ 3904 region.

As shown in FIG. 39C, the acceptor wafer may be prepared with an oxidepre-clean and deposition of a conductive barrier layer 3916 and Al—Gelayers 3914. Al—Ge eutectic layer 3914 may form an Al—Ge eutectic bondwith the conductive barrier 3910 during a thermo-compressive wafer towafer bonding process as part of the layer-transfer-flow, therebytransferring the pre-processed single crystal silicon with N+ and P−layers. Thus, a conductive path is made from the house 808 top metallayers 3920 to the now bottom N+ layer 3908 of the transferred donorwafer. Alternatively, the Al—Ge eutectic layer 3914 may be made withcopper and a copper-to-copper or copper-to-barrier layerthermo-compressive bond is formed. Likewise, a conductive path fromdonor wafer to house 808 may be made by house top metal lines 3920 ofcopper with barrier metal thermo-compressively bonded with the copperlayer 3910 directly, where a majority of the bonded surface is donorcopper to house oxide bonds and the remainder of the surface is donorcopper to house 808 copper and barrier metal bonds.

FIGS. 40A-40I are drawing illustrations of the formation of a verticalgate-all-around n-MOSFET top transistor. FIG. 40A illustrates the firststep. After the conductive path layer transfer described above, adeposition of a CMP and plasma etch stop layer 4002, such as lowtemperature SiN, may be deposited on top of the top N+ layer 3904. Forsimplicity, the conductive barrier clad Al—Ge eutectic layers 3910,3914, and 3916 are represented by conductive layer 4004 in FIG. 40A.

FIGS. 40B-H are drawn as orthographic projections (i.e., as top viewswith horizontal and vertical cross sections) to illustrate some processand topographical details. The transistor illustrated is square shapedwhen viewed from the top, but may be constructed in various rectangularshapes to provide different transistor widths and gate control effects.In addition, the square shaped transistor illustrated may beintentionally formed as a circle when viewed from the top and hence forma vertical cylinder shape, or it may become that shape during processingsubsequent to forming the vertical towers. Turning now to FIG. 40B,vertical transistor towers 4006 are mask defined and thenplasma/Reactive-ion Etching (RIE) etched thru the Chemical MechanicalPolishing (CMP) stop layer 4004, N+ layers 3904 and 3908, the P− layer3906, the conductive metal bonding layer 4004, and into the house 808oxide, and then the photoresist is removed as illustrated in FIG. 40B.This definition and etch now creates N-P-N stacks where the bottom N+layer 3908 is electrically coupled to the house metal layer 3920 throughconductive layer 4004.

The area between the towers is partially filled with oxide 4010 via aSpin On Glass (SPG) spin, cure, and etch back sequence as illustrated inFIG. 40C. Alternatively, a low temperature CVD gap fill oxide may bedeposited, then Chemically Mechanically Polished (CMP'ed) flat, and thenselectively etched back to achieve the same oxide shape 4010 as shown inFIG. 40C. The level of the oxide 4010 is constructed such that a smallamount of the bottom N+ tower layer 3908 is not covered by oxide.Alternatively, this step may also be accomplished by a conformal lowtemperature oxide CVD deposition and etch back sequence, creating aspacer profile coverage of the bottom N+ tower layer 3908.

Next, the sidewall gate oxide 4014 is formed by a low temperaturemicrowave oxidation technique, such as the TEL SPA (Tokyo ElectronLimited Slot Plane Antenna) oxygen radical plasma, stripped by wetchemicals such as dilute HF, and grown again 4014 as illustrated in FIG.40D.

The gate electrode is then deposited, such as a conformal dopedamorphous silicon layer 4018, as illustrated in FIG. 40E. The gate maskphotoresist 4020 may then be defined.

As illustrated in FIG. 40F, the gate layer 4018 is etched such that aspacer shaped gate electrode 4022 remains in regions not covered by thephotoresist 4020. The full thickness of gate layer 4018 remains underarea covered by the resist 4020 and the gate layer 4020 is also fullycleared from between the towers. Finally the photoresist 4020 isstripped. This approach minimizes the gate to drain overlap andeventually provides a clear contact connection to the gate electrode.

As illustrated in FIG. 40G, the spaces between the towers are filled andthe towers are covered with oxide 4030 by low temperature gap filldeposition and CMP.

In FIG. 40H, the via contacts 4034 to the tower N+ layer 3904 are maskedand etched, and then the via contacts 4036 to the gate electrode poly4024 are masked and etch.

The metal lines 4040 are mask defined and etched, filled with barriermetals and copper interconnect, and CMP'd in a normal interconnectscheme, thereby completing the contact via connections to the tower N+3904 and the gate electrode 4024 as illustrated in FIG. 40I.

This flow enables the formation of mono-crystalline silicon top MOStransistors that are connected to the underlying multi-metal layersemiconductor device without exposing the underlying devices andinterconnect metals to high temperature. These transistors could be usedas programming transistors of the Antifuse on layer 807, or be coupledto metal layers in wafer or layer 808 to form monolithic 3D ICs, as apass transistor for logic on wafer or layer 808, or FPGA use, or foradditional uses in a 3D semiconductor device.

Additionally, a vertical gate all around junction-less transistor may beconstructed as illustrated in FIGS. 54 and 55. The donor waferpreprocessed for the general layer transfer process is illustrated inFIG. 54. FIG. 54A is a drawing illustration of a pre-processed waferused for a layer transfer. An N− wafer 5402 is processed to have a layerof N+ 5404, by ion implantation and activation, or an N+ epitaxialgrowth. FIG. 54B is a drawing illustration of the pre-processed wafermade ready for a conductive bond layer transfer by a deposition of aconductive barrier layer 5410 such as TiN or TaN and by an implant of anatomic species, such as H+, preparing the SmartCut cleaving plane 5412in the lower part of the N+ 5404 region.

The acceptor wafer or house 808 is also prepared with an oxide pre-cleanand deposition of a conductive barrier layer 5416 and Al and Ge layersto form a Ge—Al eutectic bond 5414 during a thermo-compressive wafer towafer bonding as part of the layer-transfer-flow, thereby transferringthe pre-processed single crystal silicon of FIG. 54B with an N+ layer5404, on top of acceptor wafer or house 808, as illustrated in FIG. 54C.The N+ layer 5404 may be polished to remove damage from the cleavingprocedure. Thus, a conductive path is made from the acceptor wafer orhouse 808 top metal layers 5420 to the N+ layer 5404 of the transferreddonor wafer. Alternatively, the Al—Ge eutectic layer 5414 may be madewith copper and a copper-to-copper or copper-to-barrier layerthermo-compressive bond is formed. Likewise, a conductive path fromdonor wafer to acceptor wafer or house 808 may be made by house topmetal lines 5420 of copper with associated barrier metalthermo-compressively bonded with the copper layer 5410 directly, where amajority of the bonded surface is donor copper to house oxide bonds andthe remainder of the surface is donor copper to acceptor wafer or house808 copper and barrier metal bonds.

FIGS. 55A-55I are drawing illustrations of the formation of a verticalgate-all-around junction-less transistor utilizing the abovepreprocessed acceptor wafer or house 808 of FIG. 54C. FIG. 55Aillustrates the deposition of a CMP and plasma etch stop layer 5502,such as low temperature SiN, on top of the N+ layer 5504. Forsimplicity, the barrier clad Al—Ge eutectic layers 5410, 5414, and 5416of FIG. 54C are represented by one illustrated layer 5500.

Similarly, FIGS. 55B-H are drawn as an orthographic projection toillustrate some process and topographical details. The junction-lesstransistor illustrated is square shaped when viewed from the top, butmay be constructed in various rectangular shapes to provide differenttransistor channel thicknesses, widths, and gate control effects. Inaddition, the square shaped transistor illustrated may be intentionallyformed as a circle when viewed from the top and hence form a verticalcylinder shape, or it may become that shape during processing subsequentto forming the vertical towers. The vertical transistor towers 5506 aremask defined and then plasma/Reactive-ion Etching (RIE) etched thru theChemical Mechanical Polishing (CMP) stop layer 5502, N+ transistorchannel layer 5504, the metal bonding layer 5500, and down to theacceptor wafer or house 808 oxide, and then the photoresist is removed,as illustrated in FIG. 55B. This definition and etch now creates N+transistor channel stacks that are electrically isolated from each otheryet the bottom of N+ layer 5404 is electrically connected to the housemetal layer 5420.

The area between the towers is then partially filled with oxide 5510 viaa Spin On Glass (SPG) spin, low temperature cure, and etch back sequenceas illustrated in FIG. 55C. Alternatively, a low temperature CVD gapfill oxide may be deposited, then Chemically Mechanically Polished(CMP'ed) flat, and then selectively etched back to achieve the sameshaped 5510 as shown in FIG. 55C. Alternatively, this step may also beaccomplished by a conformal low temperature oxide CVD deposition andetch back sequence, creating a spacer profile coverage of the N+resistor tower layer 5504.

Next, the sidewall gate oxide 5514 is formed by a low temperaturemicrowave oxidation technique, such as the TEL SPA (Tokyo ElectronLimited Slot Plane Antenna) oxygen radical plasma, stripped by wetchemicals such as dilute HF, and grown again 5514 as illustrated in FIG.55D.

The gate electrode is then deposited, such as a P+ doped amorphoussilicon layer 5518, then Chemically Mechanically Polished (CMP'ed) flat,and then selectively etched back to achieve the shape 5518 as shown inFIG. 55E, and then the gate mask photoresist 5520 may be defined asillustrated in FIG. 55E.

The gate layer 5518 is etched such that the gate layer is fully clearedfrom between the towers and then the photoresist is stripped asillustrated in FIG. 55F.

The spaces between the towers are filled and the towers are covered withoxide 5530 by low temperature gap fill deposition, CMP, then anotheroxide deposition as illustrated in FIG. 55G.

In FIG. 55H, the contacts 5534 to the transistor channel tower N+ 5504are masked and etched, and then the contacts 5518 to the gate electrode5518 are masked and etch. The metal lines 5540 are mask defined andetched, filled with barrier metals and copper interconnect, and CMP'edin a normal Dual Damascene interconnect scheme, thereby completing thecontact via connections to the transistor channel tower N+ 5504 and thegate electrode 5518 as illustrated in FIG. 55I.

This flow enables the formation of mono-crystalline silicon top verticaljunction-less transistors that are connected to the underlyingmulti-metal layer semiconductor device without exposing the underlyingdevices and interconnect metals to high temperature. These junction-lesstransistors may be used as programming transistors of the Antifuse onacceptor wafer or house 808 or as a pass transistor for logic or FPGAuse, or for additional uses in a 3D semiconductor device.

Recessed Channel Array Transistors (RCATs) may be another transistorfamily that can utilize layer transfer and etch definition to constructa low-temperature monolithic 3D Integrated Circuit. The recessed channelarray transistor may sometimes be referred to as a recessed channeltransistor. Two types of RCAT device structures are shown in FIG. 66.These were described by J. Kim, et al. at the Symposium on VLSITechnology, in 2003 and 2005. Note that this prior art from Kim, et al.are for a single layer of transistors and did not use any layer transfertechniques. Their work also used high-temperature processes such assource-drain activation anneals, wherein the temperatures were above400° C. In contrast, some embodiments of the present invention employthis transistor family in a two-dimensional plane. Transistors in thisdocument, such as, for example, junction-less, recessed channel array,or depletion, with the source and the drain in the same two dimensionalplanes may be considered planar transistors. The terms horizontaltransistors, horizontally oriented transistors, or lateral transistorsmay also refer to planar transistors. Additionally, the gates oftransistors in embodiments of the present invention that include gateson two or more sides of the transistor channel may be referred to asside gates.

A layer stacking approach to construct 3D integrated circuits withstandard RCATs is illustrated in FIG. 67A-F. For an n-channel MOSFET, ap− silicon wafer 6700 may be the starting point. A buried layer of n+ Si6702 may then be implanted as shown in FIG. 67A, resulting in a layer ofp− 6703 that is at the surface of the donor wafer. An alternative is toimplant a shallow layer of n+ Si and then epitaxially deposit a layer ofp− Si 6703. To activate dopants in the n+ layer 6702, the wafer may beannealed, with standard annealing procedures such as thermal, or spike,or laser anneal.

An oxide layer 6701 may be grown or deposited, as illustrated in FIG.67B. Hydrogen is implanted into the wafer 6704 to enable “smart cut”process, as indicated in FIG. 67B.

A layer transfer process may be conducted to attach the donor wafer inFIG. 67B to a pre-processed circuits acceptor wafer 808 as illustratedin FIG. 67C. The implanted hydrogen layer 6704 may now be utilized forcleaving away the remainder of the wafer 6700.

After the cut, chemical mechanical polishing (CMP) may be performed.Oxide isolation regions 6705 may be formed and an etch process may beconducted to form the recessed channel 6706 as illustrated in FIG. 67D.This etch process may be further customized so that corners are roundedto avoid high field issues.

A gate dielectric 6707 may then be deposited, either through atomiclayer deposition or through other low-temperature oxide formationprocedures described previously. A metal gate 6708 may then be depositedto fill the recessed channel, followed by a CMP and gate patterning asillustrated in FIG. 67E.

A low temperature oxide 6709 may be deposited and planarized by CMP.Contacts 6710 may be formed to connect to all electrodes of thetransistor as illustrated in FIG. 67F. This flow enables the formationof a low temperature RCAT monolithically on top of pre-processedcircuitry 808. A p-channel MOSFET may be formed with an analogousprocess. The p and n channel RCATs may be utilized to form a monolithic3D CMOS circuit library as described later.

A layer stacking approach to construct 3D integrated circuits withspherical-RCATs (S-RCATs) is illustrated in FIG. 68A-F. For an n-channelMOSFET, a p− silicon wafer 6800 may be the starting point. A buriedlayer of n+ Si 6802 may then implanted as shown in FIG. 68A, resultingin a layer of p− 6803 at the surface of the donor wafer. An alternativeis to implant a shallow layer of n+ Si and then epitaxially deposit alayer of p− Si 6803. To activate dopants in the n+ layer 6802, the wafermay be annealed, with standard annealing procedures such as thermal, orspike, or laser anneal.

An oxide layer 6801 may be grown or deposited, as illustrated in FIG.68B. Hydrogen may be implanted into the wafer 6804 to enable “smart cut”process, as indicated in FIG. 68B.

A layer transfer process may be conducted to attach the donor wafer inFIG. 68B to a pre-processed circuits acceptor wafer 808 as illustratedin FIG. 68C. The implanted hydrogen layer 6804 may now be utilized forcleaving away the remainder of the wafer 6800. After the cut, chemicalmechanical polishing (CMP) may be performed.

Oxide isolation regions 6805 may be formed as illustrated in FIG. 68D.The eventual gate electrode recessed channel may be masked and partiallyetched, and a spacer deposition 6806 may be performed with a conformallow temperature deposition such as silicon oxide or silicon nitride or acombination.

An anisotropic etch of the spacer may be performed to leave spacermaterial only on the vertical sidewalls of the recessed gate channelopening. An isotropic silicon etch may then be conducted to form thespherical recess 6807 as illustrated in FIG. 68E. The spacer on thesidewall may be removed with a selective etch.

A gate dielectric 6808 may then be deposited, either through atomiclayer deposition or through other low-temperature oxide formationprocedures described previously. A metal gate 6809 may be deposited tofill the recessed channel, followed by a CMP and gate patterning asillustrated in FIG. 68F. The gate material may also be doped amorphoussilicon or other low temperature conductor with the proper workfunction. A low temperature oxide 6810 may be deposited and planarizedby the CMP. Contacts 6811 may be formed to connect to all electrodes ofthe transistor as illustrated in FIG. 68F.

This flow enables the formation of a low temperature S-RCATmonolithically on top of pre-processed circuitry 808. A p-channel MOSFETmay be formed with an analogous process. The p and n channel S-RCATs maybe utilized to form a monolithic 3D CMOS circuit library as describedlater. In addition, SRAM circuits constructed with RCATs may havedifferent trench depths compared to logic circuits. The RCAT and S-RCATdevices may be utilized to form BiCMOS inverters and other mixedcircuitry when the house 808 layer has conventional Bipolar JunctionTransistors and the transferred layer or layers may be utilized to formthe RCAT devices monolithically.

A planar n-channel junction-less recessed channel array transistor(JLRCAT) suitable for a 3D IC may be constructed. The JLRCAT may providean improved source and drain contact resistance, thereby allowing forlower channel doping, and the recessed channel may provide for moreflexibility in the engineering of channel lengths and characteristics,and increased immunity from process variations.

As illustrated in FIG. 151A, an N− substrate donor wafer 15100 may beprocessed to include wafer sized layers of N+ doping 15102, and N−doping 15103 across the wafer. The N+ doped layer 15102 may be formed byion implantation and thermal anneal. In addition, N− doped layer 15103may have additional ion implantation and anneal processing to provide adifferent dopant level than N− substrate 15100. N− doped layer 15103 mayalso have graded N− doping to mitigate transistor performance issues,such as, for example, short channel effects, after the formation of theJLRCAT. The layer stack may alternatively be formed by successiveepitaxially deposited doped silicon layers of N+ doping 15102 and N−doping 15103, or by a combination of epitaxy and implantation. Annealingof implants and doping may utilize optical annealing techniques or typesof Rapid Thermal Anneal (RTA or spike).

As illustrated in FIG. 151B, the top surface of donor wafer 15100 layersstack from FIG. 151A may be prepared for oxide wafer bonding with adeposition of an oxide to form oxide layer 15101 on top of N− dopedlayer 15103. A layer transfer demarcation plane (shown as dashed line)15104 may be formed by hydrogen implantation, co-implantation such ashydrogen and helium, or other methods as previously described.

As illustrated in FIG. 151C, both the donor wafer 15100 and acceptorsubstrate 808 may be prepared for wafer bonding as previously describedand then low temperature (less than approximately 400° C.) aligned andoxide to oxide bonded. Acceptor substrate 808, as described previously,may include, for example, transistors, circuitry, metal, such as, forexample, aluminum or copper, interconnect wiring, and thru layer viametal interconnect strips or pads. The portion of the donor wafer 15100and N+ doped layer 15102 that is below the layer transfer demarcationplane 15104 may be removed by cleaving or other processes as previouslydescribed, such as, for example, ion-cut or other methods. Oxide layer15101, N− layer 15103, and N+ doped layer 15122 have been layertransferred to acceptor wafer 808. Now JLRCAT transistors may be formedwith low temperature (less than approximately 400° C.) processing andmay be aligned to the acceptor wafer 808 alignment marks (not shown).

As illustrated in FIG. 151D, the transistor isolation regions 15105 maybe formed by mask defining and then plasma/RIE etching N+ doped layer15122, and N− layer 15103 to the top of oxide layer 15101 or into oxidelayer 15101. Then a low-temperature gap fill oxide may be deposited andchemically mechanically polished, with the oxide remaining in isolationregions 15105. Then the recessed channel 15106 may be mask defined andetched thru N+ doped layer 15122 and partially into N− doped layer15103. The recessed channel 15106 surfaces and edges may be smoothed byprocesses such as, for example, wet chemical, plasma/RIE etching, lowtemperature hydrogen plasma, or low temperature oxidation and striptechniques, to mitigate high field and other effects. These processsteps may form isolation regions 15105, N+ source and drain regions15132 and N− channel region 15123.

As illustrated in FIG. 151E, a gate dielectric 15107 may be formed and agate metal material may be deposited. The gate dielectric 15107 may bean atomic layer deposited (ALD) gate dielectric that is paired with awork function specific gate metal in the industry standard high k metalgate process schemes described previously. Or the gate dielectric 15107may be formed with a low temperature oxide deposition or low temperaturemicrowave plasma oxidation of the silicon surfaces and then a gate metalmaterial such as, for example, tungsten or aluminum may be deposited.Then the gate metal material may be chemically mechanically polished,and the gate area defined by masking and etching, thus forming gateelectrode 15108.

As illustrated in FIG. 151F, a low temperature thick oxide 15109 may bedeposited and planarized, and source, gate, and drain contacts, and thrulayer via (not shown) openings may be masked and etched, therebypreparing the transistors to be connected via metallization. Thus gatecontact 15111 connects to gate electrode 15108, and source & draincontacts 15110 connect to N+ source and drain regions 15132. Thru layervias (not shown) may be formed to connect to the acceptor substrateconnect strips (not shown) as previously described.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 151A through 151F are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, a p-channel JLCATT may beformed with changing the types of dopings appropriately. Moreover, thesubstrate 15100 may be p type as well as the n type described above.Further, N− doped layer 15103 may include multiple layers of differentdoping concentrations and gradients to fine tune the eventual JLRCATchannel for electrical performance and reliability characteristics, suchas, for example, off-state leakage current and on-state current.Furthermore, isolation regions 15105 may be formed by a hard maskdefined process flow, wherein a hard mask stack, such as, for example,silicon oxide and silicon nitride layers, or silicon oxide and amorphouscarbon layers. Moreover, CMOS JLRCATs may be constructed with n-JLRCATsin one mono-crystalline silicon layer and p-JLRCATs in a secondmono-crystalline layer, which may include different crystallineorientations of the mono-crystalline silicon layers, such as, forexample, <100>, <111> or <551>, and may include different contactsilicides for optimum contact resistance to p or n type source, drains,and gates. Furthermore, a back-gate or double gate structure may beformed for the JLRCAT and may utilize techniques described elsewhere inthis document. Many other modifications within the scope of theinvention will suggest themselves to such skilled persons after readingthis specification. Thus the invention is to be limited only by theappended claims.

An n-channel Trench MOSFET transistor suitable for a 3D IC may beconstructed. The trench MOSFET may provide an improved drive current andthe channel length can be tuned without area penalty. The trench MOSFETcan be formed utilizing layer transfer techniques.

As illustrated in FIG. 152A, a P− substrate donor wafer 15200 may beprocessed to include wafer sized layers of N+ doping 15204 and 15208,and P− doping 15206 across the wafer. The N+ doped layers 15204 and15208 may be formed by ion implantation and thermal anneal. In addition,P− doped layer 15206 may have additional ion implantation and annealprocessing to provide a different dopant level than P− substrate 15200.P− doped layer 15206 may also have graded P− doping to mitigatetransistor performance issues, such as, for example, short channeleffects, after the formation of the trench MOSFET. The layer stack mayalternatively be formed by successive epitaxially deposited dopedsilicon layers of N+ doping 15204, P− doping 15206, and N+ doping 15208,or by a combination of epitaxy and implantation, or other formationtechniques. Annealing of implants and doping may utilize techniques,such as, for example, optical annealing or types of Rapid Thermal Anneal(RTA or spike).

As illustrated in FIG. 152B, the top surface of donor wafer 15200 layersstack from FIG. 152A may be prepared for oxide wafer bonding with adeposition of an oxide to form oxide layer 15210 on top of N+ dopedlayer 15208. A layer transfer demarcation plane (shown as dashed line)15299 may be formed by hydrogen implantation, co-implantation such ashydrogen and helium, or other methods as previously described. The layertransfer demarcation plane 15299 may be formed within N+ layer 15204(shown) or donor wafer substrate 15200 (not shown).

As illustrated in FIG. 152C, both the donor wafer 15200 and acceptorsubstrate 808 may be prepared for wafer bonding as previously describedand then low temperature (less than approximately 400° C.) aligned andoxide to oxide bonded. Acceptor substrate 808, as described previously,may include, for example, transistors, circuitry, metal, such as, forexample, aluminum or copper, interconnect wiring, and thru layer viametal interconnect strips or pads. The portion of the donor wafer 15200and N+ doped layer 15204 that is below the layer transfer demarcationplane 152994 may be removed by cleaving or other processes as previouslydescribed, such as, for example, ion-cut or other methods. Oxide layer15210 (not shown), N+ layer 15208, P− layer 15206, and N+ doped layer15214 have been layer transferred to acceptor wafer 808. Now trenchMOSFET transistors may be formed with low temperature (less thanapproximately 400° C.) processing and may be aligned to the acceptorwafer 808 alignment marks (not shown).

As illustrated in FIG. 152D, the transistor isolation regions 15212 andMOSFET N+ source contact opening region 15216 may be formed by maskdefining and then plasma/RIE etching N+ doped layer 15214 and P− layer15206, thus forming N+ regions 15224 and P− regions 15226.

As illustrated in FIG. 152E, the transistor isolation regions 15220 maybe formed by mask defining and then plasma/RIE etching N+ doped layer15208, thus forming N+ regions 15228. Then a low-temperature gap filloxide may be deposited and chemically mechanically polished, with theoxide remaining in isolation regions 15218. A polish stop layer or hardmask stack 15260, such as, for example, silicon oxide and siliconnitride layers, or silicon oxide and amorphous carbon layers, may bedeposited.

As illustrated in FIG. 152F, gate trench 15252 may be formed by maskdefining and then plasma/RIE etching the hard mask etch stack 15260, andthen etching thru N+ doped layer 15222, P− layer 15226, and partiallyinto N+ doped layer 15228, thus forming source N+ regions 15234, P−channel regions 15236, and N+ source region 15238. The trench may haveslopes from 45 to 160 degrees at vertices 15250, 135 degrees is shown,and may also be accomplished by wet etching techniques. The gate trench15252 surfaces and edges may be smoothed by processes such as, forexample, wet chemical, plasma/RIE etching, low temperature hydrogenplasma, or low temperature oxidation and strip techniques, to mitigatehigh field and other effects. The hard mask etch stack 15260 may also bethus formed into hard mask etch stack regions 15262.

As illustrated in FIG. 152G, a gate dielectric 15253 may be formed and agate metal material may be deposited. The gate dielectric 15253 may bean atomic layer deposited (ALD) gate dielectric that is paired with awork function specific gate metal 15254 in the industry standard high kmetal gate process schemes described previously. Or the gate dielectric15253 may be formed with a low temperature oxide deposition or lowtemperature microwave plasma oxidation of the silicon surfaces and thena gate metal material 15254, such as, for example, tungsten or aluminum,may be deposited.

As illustrated in FIG. 152H, the gate metal material 15254 may bechemically mechanically polished, thus forming gate electrode 15256 andthinned polish stop regions or hard mask etch stack regions 15263. Thegate electrode 15256 may also be defined by masking and etching.

As illustrated in FIG. 152I, a low temperature thick oxide may bedeposited and planarized, and source, gate, and drain contacts, and thrulayer via openings may be masked and etched, thereby preparing thetransistors to be connected via metallization, thus forming oxideregions 15285. Thus gate contact 15274 connects to gate electrode 15256,drain contacts 15270 connect to N+ drain regions 15234, and sourcecontact 15272 connect to N+ source region 15238. Thru layer vias 15280may be formed to connect to the acceptor substrate 808 metal connectstrips 15290 as previously described.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 152A through 152I are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, a p-channel trench MOSFETmay be formed with changing the types of dopings appropriately.Moreover, the substrate 15200 may be n type as well as the p typedescribed above. Further, P− doped layer 15206 may include multiplelayers of different doping concentrations and gradients to fine tune theeventual trench MOSFET channel for electrical performance andreliability characteristics, such as, for example, off-state leakagecurrent and on-state current. Furthermore, P− regions 15226 may bepreferentially side etched to recess and narrow the eventual P− channelregions 15236 so that gate control may be more effective. The recess maybe filled with oxide for improved N+ source 15238 to N+ drain 15234isolation. Many other modifications within the scope of the inventionwill suggest themselves to such skilled persons after reading thisspecification. Thus the invention is to be limited only by the appendedclaims.

3D memory device structures may also be constructed in layers ofmono-crystalline silicon and take advantage of pre-processing a donorwafer by forming wafer sized layers of various materials without aprocess temperature restriction, then layer transferring thepre-processed donor wafer to the acceptor wafer, followed by someoptional processing steps, and repeating this procedure multiple times,and then processing with either low temperature (below approximately400° C.) or high temperature (greater than approximately 400° C.) afterthe final layer transfer to form memory device structures, such as, forexample, transistors or memory bit cells, on or in the multipletransferred layers that may be physically aligned and may beelectrically coupled to the acceptor wafer. The term memory cells mayalso describe as memory bit cells in this document.

Novel monolithic 3D Dynamic Random Access Memories (DRAMs) may beconstructed in the above manner. Some embodiments of this presentinvention utilize the floating body DRAM type.

Floating-body DRAM is a next generation DRAM being developed by manycompanies such as Innovative Silicon, Hynix, and Toshiba. Thesefloating-body DRAMs store data as charge in the floating body of an SOIMOSFET or a multi-gate MOSFET. Further details of a floating body DRAMand its operation modes can be found in U.S. Pat. Nos. 7,541,616,7,514,748, 7,499,358, 7,499,352, 7,492,632, 7,486,563, 7,477,540, and7,476,939, besides other literature. A monolithic 3D integrated DRAM canbe constructed with floating-body transistors. Prior art forconstructing monolithic 3D DRAMs used planar transistors wherecrystalline silicon layers were formed with either selective epitechnology or laser recrystallization. Both selective epi technology andlaser recrystallization may not provide perfectly single crystal siliconand often require a high thermal budget. A description of theseprocesses is given in the book entitled “Integrated InterconnectTechnologies for 3D Nanoelectronic Systems” by Bakir and Meindl.

As illustrated in FIG. 97 the fundamentals of operating a floating bodyDRAM are described. In order to store a ‘1’ bit, excess holes 9702 mayexist in the floating body region 9720 and change the threshold voltageof the memory cell transistor including source 9704, gate 9706, drain9708, floating body 9720, and buried oxide (BOX) 9718. This is shown inFIG. 97( a). The ‘0’ bit corresponds to no charge being stored in thefloating body 9720 and affects the threshold voltage of the memory celltransistor including source 9710, gate 9712, drain 9714, floating body9720, and buried oxide (BOX) 9716. This is shown in FIG. 97( b). Thedifference in threshold voltage between the memory cell transistordepicted in FIG. 97( a) and FIG. 97( b) manifests itself as a change inthe drain current 9734 of the transistor at a particular gate voltage9736. This is described in FIG. 97( c). This current differential 9730may be sensed by a sense amplifier circuit to differentiate between ‘0’and ‘1’ states and thus function as a memory bit.

As illustrated in FIGS. 98A to 98H, a horizontally-oriented monolithic3D DRAM that utilizes two masking steps per memory layer may beconstructed that is suitable for 3D IC manufacturing.

As illustrated in FIG. 98A, a P− substrate donor wafer 9800 may beprocessed to comprise a wafer sized layer of P− doping 9804. The P−layer 9804 may have the same or a different dopant concentration thanthe P− substrate 9800. The P− doping layer 9804 may be formed by ionimplantation and thermal anneal. A screen oxide 9801 may be grown beforethe implant to protect the silicon from implant contamination and toprovide an oxide surface for later wafer to wafer bonding.

As illustrated in FIG. 98B, the top surface of donor wafer 9800 may beprepared for oxide to oxide wafer bonding with a deposition of an oxide9802 or by thermal oxidation of the P− layer 9804 to form oxide layer9802, or a re-oxidation of implant screen oxide 9801. A layer transferdemarcation plane 9899 (shown as a dashed line) may be formed in donorwafer 9800 or P− layer 9804 (shown) by hydrogen implantation 9807 orother methods as previously described. Both the donor wafer 9800 andacceptor wafer 9810 may be prepared for wafer bonding as previouslydescribed and then bonded, preferably at a low temperature (less thanapproximately 400° C.) to minimize stresses. The portion of the P− layer9804 and the P− donor wafer substrate 9800 that are above the layertransfer demarcation plane 9899 may be removed by cleaving andpolishing, or other processes as previously described, such as ion-cutor other methods.

As illustrated in FIG. 98C, the remaining P− doped layer 9804′, andoxide layer 9802 have been layer transferred to acceptor wafer 9810.Acceptor wafer 9810 may comprise peripheral circuits such that they canwithstand an additional rapid-thermal-anneal (RTA) and still remainoperational and retain good performance. For this purpose, theperipheral circuits may be formed such that they have not had an RTA foractivating dopants or have had a weak RTA. Also, the peripheral circuitsmay utilize a refractory metal such as tungsten that can withstand hightemperatures greater than approximately 400° C. The top surface of P−doped layer 9804′ may be chemically or mechanically polished smooth andflat. Now transistors may be formed and aligned to the acceptor wafer9810 alignment marks (not shown).

As illustrated in FIG. 98D shallow trench isolation (STI) oxide regions(not shown) may be lithographically defined and plasma/RIE etched to atleast the top level of oxide layer 9802 removing regions of P−mono-crystalline silicon layer 9804′. A gap-fill oxide may be depositedand CMP'ed flat to form conventional STI oxide regions and P-dopedmono-crystalline silicon regions (not shown) for forming thetransistors. Threshold adjust implants may or may not be performed atthis time. A gate stack 9824 may be formed with a gate dielectric, suchas thermal oxide, and a gate metal material, such as polycrystallinesilicon. Alternatively, the gate oxide may be an atomic layer deposited(ALD) gate dielectric that is paired with a work function specific gatemetal according to an industry standard of high k metal gate processschemes described previously. Or the gate oxide may be formed with arapid thermal oxidation (RTO), a low temperature oxide deposition or lowtemperature microwave plasma oxidation of the silicon surfaces and thena gate material such as tungsten or aluminum may be deposited. Gatestack self-aligned LDD (Lightly Doped Drain) and halo punch-thruimplants may be performed at this time to adjust junction and transistorbreakdown characteristics. A conventional spacer deposition of oxideand/or nitride and a subsequent etchback may be done to form implantoffset spacers (not shown) on the gate stacks 9824. Then a self-alignedN+ source and drain implant may be performed to create transistor sourceand drains 9820 and remaining P− silicon NMOS transistor channels 9828.High temperature anneal steps may or may not be done at this time toactivate the implants and set initial junction depths. Finally, theentire structure may be covered with a gap fill oxide 9850, which may beplanarized with chemical mechanical polishing. The oxide surface may beprepared for oxide to oxide wafer bonding as previously described.

As illustrated in FIG. 98E, the transistor layer formation, bonding toacceptor wafer 9810 oxide 9850, and subsequent transistor formation asdescribed in FIGS. 98A to 98D may be repeated to form the second tier9830 of memory transistors. After all the memory layers are constructed,a rapid thermal anneal (RTA) may be conducted to activate the dopants inall of the memory layers and in the acceptor substrate 9810 peripheralcircuits. Alternatively, optical anneals, such as, for example, a laserbased anneal, may be performed.

As illustrated in FIG. 98F, contacts and metal interconnects may beformed by lithography and plasma/RIE etch. Bit line (BL) contacts 9840electrically couple the memory layers' transistor N+ regions on thetransistor drain side 9854, and the source line contact 9842electrically couples the memory layers' transistor N+ regions on thetransistors source side 9852. The bit-line (BL) wiring 9848 andsource-line (SL) wiring 9846 electrically couples the bit-line contacts9840 and source-line contacts 9842 respectively. The gate stacks, suchas 9834, may be connected with a contact and metallization (not shown)to form the word-lines (WLs). A thru layer via 9860 (not shown) may beformed to electrically couple the BL, SL, and WL metallization to theacceptor substrate 9810 peripheral circuitry via an acceptor wafer metalconnect pad 1980 (not shown).

As illustrated in FIG. 98G, a top-view layout a section of the top ofthe memory array is shown where WL wiring 9864 and SL wiring 9865 may beperpendicular to the BL wiring 9866.

As illustrated in FIG. 98H, a schematic of each single layer of the DRAMarray shows the connections for WLs, BLs and SLs at the array level. Themultiple layers of the array share BL and SL contacts, but each layerhas its own unique set of WL connections to allow each bit to beaccessed independently of the others.

This flow enables the formation of a horizontally-oriented monolithic 3DDRAM array that utilizes two masking steps per memory layer and isconstructed by layer transfers of wafer sized doped mono-crystallinesilicon layers and this 3D DRAM array may be connected to an underlyingmulti-metal layer semiconductor device, which may or may not contain theperipheral circuits, used to control the DRAM's read and writefunctions.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 98A through 98H are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the transistors may be ofanother type such as RCATs, or junction-less. Or the contacts mayutilize doped poly-crystalline silicon, or other conductive materials.Or the stacked memory layer may be connected to a periphery circuit thatis above the memory stack. Many other modifications within the scope ofthe invention will suggest themselves to such skilled persons afterreading this specification. Thus the invention is to be limited only bythe appended claims.

As illustrated in FIGS. 99A to 99M, a horizontally-oriented monolithic3D DRAM that utilizes one masking step per memory layer may beconstructed that is suitable for 3D IC.

As illustrated in FIG. 99A, a silicon substrate with peripheralcircuitry 9902 may be constructed with high temperature (greater thanapproximately 400° C.) resistant wiring, such as Tungsten. Theperipheral circuitry substrate 9902 may comprise memory control circuitsas well as circuitry for other purposes and of various types, such asanalog, digital, radio-frequency (RF), or memory. The peripheralcircuitry substrate 9902 may comprise peripheral circuits that canwithstand an additional rapid-thermal-anneal (RTA) and still remainoperational and retain good performance. For this purpose, theperipheral circuits may be formed such that they have been subject to aweak RTA or no RTA for activating dopants. The top surface of theperipheral circuitry substrate 9902 may be prepared for oxide waferbonding with a deposition of a silicon oxide 9904, thus forming acceptorwafer 2414.

As illustrated in FIG. 99B, a mono-crystalline silicon donor wafer 9912may be optionally processed to comprise a wafer sized layer of P− doping(not shown) which may have a different dopant concentration than the P−substrate 9906. The P− doping layer may be formed by ion implantationand thermal anneal. A screen oxide 9908 may be grown or deposited priorto the implant to protect the silicon from implant contamination and toprovide an oxide surface for later wafer to wafer bonding. A layertransfer demarcation plane 9910 (shown as a dashed line) may be formedin donor wafer 9912 within the P− substrate 9906 or the P− doping layer(not shown) by hydrogen implantation or other methods as previouslydescribed. Both the donor wafer 9912 and acceptor wafer 9914 may beprepared for wafer bonding as previously described and then bonded atthe surfaces of oxide layer 9904 and oxide layer 9908, at a lowtemperature (less than approximately 400° C.) preferred for loweststresses, or a moderate temperature (less than approximately 900° C.).

As illustrated in FIG. 99C, the portion of the P− layer (not shown) andthe P− wafer substrate 9906 that are above the layer transferdemarcation plane 9910 may be removed by cleaving and polishing, orother processes as previously described, such as, for example, ion-cutor other methods, thus forming the remaining mono-crystalline silicon P−layer 9906′. Remaining P− layer 9906′ and oxide layer 9908 have beenlayer transferred to acceptor wafer 9914. The top surface of P− layer9906′ may be chemically or mechanically polished smooth and flat. Nowtransistors or portions of transistors may be formed and aligned to theacceptor wafer 9914 alignment marks (not shown).

As illustrated in FIG. 99D, N+ silicon regions 9916 may belithographically defined and N type species, such as Arsenic, may be ionimplanted into P− silicon layer 9906′. This also forms remaining regionsof P− silicon 9918.

As illustrated in FIG. 99E, oxide layer 9920 may be deposited to preparethe surface for later oxide to oxide bonding, leading to the formationof the first Si/SiO2 layer 9922 which includes silicon oxide layer 9920,N+ silicon regions 9916, and P− silicon regions 9918.

As illustrated in FIG. 99F, additional Si/SiO2 layers, such as secondSi/SiO2 layer 9924 and third Si/SiO2 layer 9926, may each be formed asdescribed in FIGS. 99A to 99E. Oxide layer 9929 may be deposited. Afterall the memory layers are constructed, a rapid thermal anneal (RTA) maybe conducted to activate the dopants in substantially all of the memorylayers 9922, 9924, 9926 and in the peripheral circuits 9902.Alternatively, optical anneals, such as, for example, a laser basedanneal, may be performed.

As illustrated in FIG. 99G, oxide layer 9929, third Si/SiO2 layer 9926,second Si/SiO2 layer 9924 and first Si/SiO2 layer 9922 may belithographically defined and plasma/RIE etched to form a portion of thememory cell structure. The etching may form regions of P− silicon 9918′,which will form the floating body transistor channels, and N+ siliconregions 9916′, which form the source, drain and local source lines.Thus, these transistor elements or portions have been defined by acommon lithography step, which also may be described as a singlelithography step, same lithography step, or one lithography step.

As illustrated in FIG. 99H, a gate dielectric and gate electrodematerial may be deposited, planarized with a chemical mechanical polish(CMP), and then lithographically defined and plasma/RIE etched to formgate dielectric regions 9928 which may be self-aligned to and covered bygate electrodes 9930 (shown), or may substantially cover the entiresilicon/oxide multi-layer structure. The gate electrode 9930 and gatedielectric 9928 stack may be sized and aligned such that P− siliconregions 9918′ are substantially completely covered. The gate stackcomprised of gate electrode 9930 and gate dielectric 9928 may be formedwith a gate dielectric, such as thermal oxide, and a gate electrodematerial, such as polycrystalline silicon. Alternatively, the gatedielectric may be an atomic layer deposited (ALD) material that ispaired with a work function specific gate metal according to an industrystandard of high k metal gate process schemes described previously.Further the gate dielectric may be formed with a rapid thermal oxidation(RTO), a low temperature oxide deposition or low temperature microwaveplasma oxidation of the silicon surfaces and then a gate electrode suchas tungsten or aluminum may be deposited.

As illustrated in FIG. 99I, substantially the entire structure may becovered with a gap fill oxide 9932, which may be planarized withchemical mechanical polishing. The oxide 9932 is shown transparent inthe figure for clarity, along with word-line regions (WL) 9950, coupledwith and composed of gate electrodes 9930, and source-line regions (SL)9952, composed of indicated N+ silicon regions 9916′.

As illustrated in FIG. 99J, bit-line (BL) contacts 9934 may belithographically defined, etched along with plasma/RIE, and processed bya photoresist removal. Afterwards, metal, such as copper, aluminum, ortungsten, may be deposited to fill the contact and subsequently etchedor polished to the top of oxide 9932. Each BL contact 9934 may be sharedamong substantially all layers of memory, shown as three layers ofmemory in FIG. 99J. A thru layer via 9960 (not shown) may be formed toelectrically couple the BL, SL, and WL metallization to the acceptorsubstrate 9914 peripheral circuitry via an acceptor wafer metal connectpad 9980 (not shown).

As illustrated in FIG. 99K, BL metal lines 9936 may be formed andconnected to the associated BL contacts 9934. Contacts and associatedmetal interconnect lines (not shown) may be formed for the WL and SL atthe memory array edges. SL contacts can be made into stair-likestructures using techniques described in “Bit Cost Scalable Technologywith Punch and Plug Process for Ultra High Density Flash Memory,” 2007IEEE Symposium on VLSI Technology, pp. 14-15, 12-14 Jun. 2007 by Tanaka,H.; Kido, M.; Yahashi, K.; Oomura, M.; et al.

As illustrated in FIGS. 99L, 99L1 and 99L2, cross section cut II of FIG.99L is shown in FIG. 99L1, and cross section cut III of FIG. 99L isshown in FIG. 99L2. BL metal line 9936, oxide 9932, BL contact 9934, WLregions 9950, gate dielectric 9928, P− silicon regions 9918′, andperipheral circuits substrate 9902 are shown in FIG. 99L1. The BLcontact 9934 connects to one side of the three levels of floating bodytransistors that may be comprised of two N+ silicon regions 9916′ ineach level with their associated P− silicon region 9918′. BL metal lines9936, oxide 9932, gate electrode 9930, gate dielectric 9928, P− siliconregions 9918′, interlayer oxide region (‘ox’), and peripheral circuitssubstrate 9902 are shown in FIG. 99L2. The gate electrode 9930 is commonto substantially all six P− silicon regions 9918′ and forms sixtwo-sided gated floating body transistors.

As illustrated in FIG. 99M, a single exemplary floating body transistorwith two gates on the first Si/SiO2 layer 9922 may include P− siliconregion 9918′ (functioning as the floating body transistor channel), N+silicon regions 9916′ (functioning as source and drain), and two gateelectrodes 9930 with associated gate dielectrics 9928. The transistormay be electrically isolated from beneath by oxide layer 9908.

This flow enables the formation of a horizontally-oriented monolithic 3DDRAM that utilizes one masking step per memory layer constructed bylayer transfers of wafer sized doped mono-crystalline silicon layers andthis 3D DRAM may be connected to an underlying multi-metal layersemiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 99A through 99M are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the transistors may be ofanother type such as RCATs, or junction-less. Or the contacts mayutilize doped poly-crystalline silicon, or other conductive materials.Or the stacked memory layers may be connected to a periphery circuitthat is above the memory stack. Or Si/SiO2 layers 9922, 9924 and 9926may be annealed layer-by-layer as soon as their associated implantationsare complete by using a laser anneal system. Many other modificationswithin the scope of the invention will suggest themselves to suchskilled persons after reading this specification. Thus the invention isto be limited only by the appended claims.

As illustrated in FIGS. 100A to 100L, a horizontally-oriented monolithic3D DRAM that utilizes zero additional masking steps per memory layer bysharing mask steps after substantially all the layers have beentransferred may be constructed. The 3D DRAM is suitable for 3D ICmanufacturing.

As illustrated in FIG. 100A, a silicon substrate with peripheralcircuitry 10002 may be constructed with high temperature (greater thanapproximately 400° C.) resistant wiring, such as Tungsten. Theperipheral circuitry substrate 10002 may comprise memory controlcircuits as well as circuitry for other purposes and of various types,such as analog, digital, RF, or memory. The peripheral circuitrysubstrate 10002 may include peripheral circuits that can withstand anadditional rapid-thermal-anneal (RTA) and still remain operational andretain good performance. For this purpose, the peripheral circuits maybe formed such that they have been subject to a weak RTA or no RTA foractivating dopants. The top surface of the peripheral circuitrysubstrate 10002 may be prepared for oxide wafer bonding with adeposition of a silicon oxide 10004, thus forming acceptor wafer 10014.

As illustrated in FIG. 100B, a mono-crystalline silicon donor wafer10012 may be processed to comprise a wafer sized layer of P− doping (notshown) which may have a different dopant concentration than the P−substrate 10006. The P− doping layer may be formed by ion implantationand thermal anneal. A screen oxide 10008 may be grown or deposited priorto the implant to protect the silicon from implant contamination and toprovide an oxide surface for later wafer to wafer bonding. A layertransfer demarcation plane 10010 (shown as a dashed line) may be formedin donor wafer 10012 within the P− substrate 10006 or the P− dopinglayer (not shown) by hydrogen implantation or other methods aspreviously described. Both the donor wafer 10012 and acceptor wafer10014 may be prepared for wafer bonding as previously described and thenbonded at the surfaces of oxide layer 10004 and oxide layer 10008, at alow temperature (less than approximately 400° C.) preferred for loweststresses, or a moderate temperature (less than approximately 900° C.).

As illustrated in FIG. 100C, the portion of the P− layer (not shown) andthe P− wafer substrate 10006 that are above the layer transferdemarcation plane 10010 may be removed by cleaving and polishing, orother processes as previously described, such as ion-cut or othermethods, thus forming the remaining mono-crystalline silicon P− layer10006′. Remaining P− layer 10006′ and oxide layer 10008 have been layertransferred to acceptor wafer 10014. The top surface of P− layer 10006′may be chemically or mechanically polished smooth and flat. Nowtransistors or portions of transistors may be formed and aligned to theacceptor wafer 10014 alignment marks (not shown). Oxide layer 10020 maybe deposited to prepare the surface for later oxide to oxide bonding.This now forms the first Si/SiO2 layer 10023 which includes siliconoxide layer 10020, P− silicon layer 10006′, and oxide layer 10008.

As illustrated in FIG. 100D, additional Si/SiO2 layers, such as secondSi/SiO2 layer 10025 and third Si/SiO2 layer 10027, may each be formed asdescribed in FIGS. 100A to 100C. Oxide layer 10029 may be deposited toelectrically isolate the top silicon layer.

As illustrated in FIG. 100E, oxide 10029, third Si/SiO2 layer 10027,second Si/SiO2 layer 10025 and first Si/SiO2 layer 10023 may belithographically defined and plasma/RIE etched to form a portion of thememory cell structure, which now includes regions of P− silicon 10016and oxide 10022. Thus, these transistor elements or portions have beendefined by a common lithography step, which also may be described as asingle lithography step, same lithography step, or one lithography step.

As illustrated in FIG. 100F, a gate dielectric and gate electrodematerial may be deposited, planarized with a chemical mechanical polish(CMP), and then lithographically defined and plasma/RIE etched to formgate dielectric regions 10028 which may either be self-aligned to andcovered by gate electrodes 10030 (shown), or cover the entiresilicon/oxide multi-layer structure. The gate stack including gateelectrode 10030 and gate dielectric 10028 may be formed with a gatedielectric, such as, for example, thermal oxide, and a gate electrodematerial, such as poly-crystalline silicon. Alternatively, the gatedielectric may be an atomic layer deposited (ALD) material that ispaired with a work function specific gate metal according to an industrystandard of high k metal gate process schemes described previously. Orthe gate dielectric may be formed with a rapid thermal oxidation (RTO),a low temperature oxide deposition or low temperature microwave plasmaoxidation of the silicon surfaces and then a gate electrode such as, forexample, tungsten or aluminum may be deposited.

As illustrated in FIG. 100G, N+ silicon regions 10026 may be formed in aself-aligned manner to the gate electrodes 10030 by ion implantation ofan N type species, such as Arsenic, into the regions of P− silicon 10016that are not blocked by the gate electrodes 10030. This also formsremaining regions of P− silicon 10017 (not shown) in the gate electrode10030 blocked areas. Different implant energies or angles, or multiplesof each, may be utilized to place the N type species into each layer ofP− silicon regions 10016. Spacers (not shown) may be utilized duringthis multi-step implantation process and layers of silicon present indifferent layers of the stack may have different spacer widths toaccount for the differing lateral straggle of N type species implants.Bottom layers, such as 10023, could have larger spacer widths than toplayers, such as, for example, 10027. Alternatively, angular ionimplantation with substrate rotation may be utilized to compensate forthe differing implant straggle. The top layer implantation may have aslanted angle, rather than perpendicular, to the wafer surface and henceland ions slightly underneath the gate electrode 10030 edges and closelymatch a more perpendicular lower layer implantation which may land ionsslightly underneath the gate electrode 10030 edge due to the straggleeffects of the greater implant energy needed to reach the lower layer. Arapid thermal anneal (RTA) may be conducted to activate the dopants insubstantially all of the memory layers 10023, 10025, 10027 and in theperipheral circuits 10002. Alternatively, optical anneals, such as, forexample, a laser based anneal, may be performed.

As illustrated in FIG. 100H, the entire structure may be covered with agap fill oxide 10032, which be planarized with chemical mechanicalpolishing. The oxide 10032 is shown transparent in the figure forclarity. Word-line regions (WL) 10050, coupled with and composed of gateelectrodes 10030, and source-line regions (SL) 10052, composed ofindicated N+ silicon regions 10026, are shown.

As illustrated in FIG. 100I, bit-line (BL) contacts 10034 may belithographically defined, etched with plasma/RIE, and processed by aphotoresist removal. Afterwards, metal, such as, for example, copper,aluminum, or tungsten, may be deposited to fill the contact and etchedor polished to the top of oxide 10032. Each BL contact 10034 may beshared among substantially all layers of memory, shown as three layersof memory in FIG. 100I. A thru layer via 10060 (not shown) may be formedto electrically couple the BL, SL, and WL metallization to the acceptorsubstrate 10014 peripheral circuitry via an acceptor wafer metal connectpad 10080 (not shown).

As illustrated in FIG. 100J, BL metal lines 10036 may be formed andconnect to the associated BL contacts 10034. Contacts and associatedmetal interconnect lines (not shown) may be formed for the WL and SL atthe memory array edges.

FIG. 100K1 shows a cross-sectional cut II of FIG. 100K, while FIG. 100K2shows a cross-sectional cut III of FIG. 100K. FIG. 100K1 shows BL metalline 10036, oxide 10032, BL contact 10034, WL regions 10050, gatedielectric 10028, N+ silicon regions 10026, P− silicon regions 10017,and peripheral circuits substrate 10002. The BL contact 10034 couples toone side of the three levels of floating body transistors that mayinclude two N+ silicon regions 10026 in each level with their associatedP− silicon region 10017. FIG. 100K2 shows BL metal lines 10036, oxide10032, gate electrode 10030, gate dielectric 10028, P− silicon regions10017, interlayer oxide region (‘ox’), and peripheral circuits substrate10002. The gate electrode 10030 is common to substantially all six P−silicon regions 10017 and forms six two-sided gated floating bodytransistors.

As illustrated in FIG. 100M, a single exemplary floating body two gatetransistor on the first Si/SiO2 layer 10023 may include P− siliconregion 10017 (functioning as the floating body transistor channel), N+silicon regions 10026 (functioning as source and drain), and two gateelectrodes 10030 with associated gate dielectrics 10028. The transistoris electrically isolated from beneath by oxide layer 10008.

This flow may enable the formation of a horizontally-oriented monolithic3D DRAM that utilizes zero additional masking steps per memory layer andis constructed by layer transfers of wafer sized doped mono-crystallinesilicon layers and may be connected to an underlying multi-metal layersemiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 100A through 100L are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the transistors may be ofanother type such as RCATs, or junction-less. Additionally, the contactsmay utilize doped poly-crystalline silicon, or other conductivematerials. Moreover, the stacked memory layer may be connected to aperiphery circuit that is above the memory stack. Further, each gate ofthe double gate 3D DRAM can be independently controlled for bettercontrol of the memory cell. Many other modifications within the scope ofthe invention will suggest themselves to such skilled persons afterreading this specification. Thus the invention is to be limited only bythe appended claims.

Novel monolithic 3D memory technologies utilizing material resistancechanges may be constructed in a similar manner. There are many types ofresistance-based memories including phase change memory, Metal Oxidememory, resistive RAM (RRAM), memristors, solid-electrolyte memory,ferroelectric RAM, MRAM, etc. Background information on theseresistive-memory types is given in “Overview of candidate devicetechnologies for storage-class memory,” IBM Journal of Research andDevelopment, vol. 52, no. 4.5, pp. 449-464, July 2008 by Burr, G. W.,et. al. The contents of this document are incorporated in thisspecification by reference.

As illustrated in FIGS. 101A to 101K, a resistance-based zero additionalmasking steps per memory layer 3D memory may be constructed that issuitable for 3D IC manufacturing. This 3D memory utilizes junction-lesstransistors and has a resistance-based memory element in series with aselect or access transistor.

As illustrated in FIG. 101A, a silicon substrate with peripheralcircuitry 10102 may be constructed with high temperature (greater thanapproximately 400° C.) resistant wiring, such as, for example, Tungsten.The peripheral circuitry substrate 10102 may include memory controlcircuits as well as circuitry for other purposes and of various types,such as, for example, analog, digital, RF, or memory. The peripheralcircuitry substrate 10102 may include peripheral circuits that canwithstand an additional rapid-thermal-anneal (RTA) and still remainoperational and retain good performance. For this purpose, theperipheral circuits may be formed such that they have had a weak RTA orno RTA for activating dopants. The top surface of the peripheralcircuitry substrate 10102 may be prepared for oxide wafer bonding with adeposition of a silicon oxide 10104, thus forming acceptor wafer 10114.

As illustrated in FIG. 101B, a mono-crystalline silicon donor wafer10112 may be optionally processed to include a wafer sized layer of N+doping (not shown) which may have a different dopant concentration thanthe N+ substrate 10106. The N+ doping layer may be formed by ionimplantation and thermal anneal. A screen oxide 10108 may be grown ordeposited prior to the implant to protect the silicon from implantcontamination and to provide an oxide surface for later wafer to waferbonding. A layer transfer demarcation plane 10110 (shown as a dashedline) may be formed in donor wafer 10112 within the N+ substrate 10106or the N+ doping layer (not shown) by hydrogen implantation or othermethods as previously described. Both the donor wafer 10112 and acceptorwafer 10114 may be prepared for wafer bonding as previously describedand then bonded at the surfaces of oxide layer 10104 and oxide layer10108, at a low temperature (less than approximately 400° C.) preferredfor lowest stresses, or a moderate temperature (less than approximately900° C.).

As illustrated in FIG. 101C, the portion of the N+ layer (not shown) andthe N+ wafer substrate 10106 that are above the layer transferdemarcation plane 10110 may be removed by cleaving and polishing, orother processes as previously described, such as, for example, ion-cutor other methods, thus forming the remaining mono-crystalline silicon N+layer 10106′. Remaining N+ layer 10106′ and oxide layer 10108 have beenlayer transferred to acceptor wafer 10114. The top surface of N+ layer10106′ may be chemically or mechanically polished smooth and flat. Nowtransistors or portions of transistors may be formed and aligned to theacceptor wafer 10114 alignment marks (not shown). Oxide layer 10120 maybe deposited to prepare the surface for later oxide to oxide bonding,leading to the formation of the first Si/SiO2 layer 10123 that includessilicon oxide layer 10120, N+ silicon layer 10106′, and oxide layer10108.

As illustrated in FIG. 101D, additional Si/SiO2 layers, such as, forexample, second Si/SiO2 layer 10125 and third Si/SiO2 layer 10127, mayeach be formed as described in FIGS. 101A to 101C. Oxide layer 10129 maybe deposited to electrically isolate the top N+ silicon layer.

As illustrated in FIG. 101E, oxide 10129, third Si/SiO2 layer 10127,second Si/SiO2 layer 10125 and first Si/SiO2 layer 10123 may belithographically defined and plasma/RIE etched to form a portion of thememory cell structure, which now includes regions of N+ silicon 10126and oxide 10122. Thus, these transistor elements or portions have beendefined by a common lithography step, which also may be described as asingle lithography step, same lithography step, or one lithography step.

As illustrated in FIG. 101F, a gate dielectric and gate electrodematerial may be deposited, planarized with a chemical mechanical polish(CMP), and then lithographically defined and plasma/RIE etched to formgate dielectric regions 10128 which may either be self-aligned to andcovered by gate electrodes 10130 (shown), or cover the entire N+ silicon10126 and oxide 10122 multi-layer structure. The gate stack includinggate electrode 10130 and gate dielectric 10128 may be formed with a gatedielectric, such as, for example, thermal oxide, and a gate electrodematerial, such as, for example, poly-crystalline silicon. Alternatively,the gate dielectric may be an atomic layer deposited (ALD) material thatis paired with a work function specific gate metal according to anindustry standard of high k metal gate process schemes describedpreviously. Moreover, the gate dielectric may be formed with a rapidthermal oxidation (RTO), a low temperature oxide deposition or lowtemperature microwave plasma oxidation of the silicon surfaces and thena gate electrode such as, for example, tungsten or aluminum may bedeposited.

As illustrated in FIG. 101G, the entire structure may be covered with agap fill oxide 10132, which may be planarized with chemical mechanicalpolishing. The oxide 10132 is shown transparent in the figure forclarity, along with word-line regions (WL) 10150, coupled with andcomposed of gate electrodes 10130, and source-line regions (SL) 10152,composed of N+ silicon regions 10126.

As illustrated in FIG. 101H, bit-line (BL) contacts 10134 may belithographically defined, etched along with plasma/RIE through oxide10132, the three N+ silicon regions 10126, and associated oxide verticalisolation regions to connect all memory layers vertically. BL contacts10134 may then be processed by a photoresist removal. Resistance changememory material 10138, such as, for example, hafnium oxide, may then bedeposited, preferably with atomic layer deposition (ALD). The electrodefor the resistance change memory element may then be deposited by ALD toform the electrode/BL contact 10134. The excess deposited material maybe polished to planarity at or below the top of oxide 10132. Each BLcontact 10134 with resistive change material 10138 may be shared amongsubstantially all layers of memory, shown as three layers of memory inFIG. 101H.

As illustrated in FIG. 101I, BL metal lines 10136 may be formed andconnect to the associated BL contacts 10134 with resistive changematerial 10138. Contacts and associated metal interconnect lines (notshown) may be formed for the WL and SL at the memory array edges. A thrulayer via 10160 (not shown) may be formed to electrically couple the BL,SL, and WL metallization to the acceptor substrate 10114 peripheralcircuitry via an acceptor wafer metal connect pad 10180 (not shown).

FIG. 101J1 shows a cross sectional cut II of FIG. 101J, while FIG. 101J2shows a cross-sectional cut III of FIG. 101J. FIG. 101J1 shows BL metalline 10136, oxide 10132, BL contact/electrode 10134, resistive changematerial 10138, WL regions 10150, gate dielectric 10128, N+ siliconregions 10126, and peripheral circuits substrate 10102. The BLcontact/electrode 10134 couples to one side of the three levels ofresistive change material 10138. The other side of the resistive changematerial 10138 is coupled to N+ regions 10126. FIG. 101J2 shows BL metallines 10136, oxide 10132, gate electrode 10130, gate dielectric 10128,N+ silicon regions 10126, interlayer oxide region (‘ox’), and peripheralcircuits substrate 10102. The gate electrode 10130 is common tosubstantially all six N+ silicon regions 10126 and forms six two-sidedgated junction-less transistors as memory select transistors.

As illustrated in FIG. 101K, a single exemplary two-sided gatejunction-less transistor on the first Si/SiO2 layer 10123 may include N+silicon region 10126 (functioning as the source, drain, and transistorchannel), and two gate electrodes 10130 with associated gate dielectrics10128. The transistor is electrically isolated from beneath by oxidelayer 10108.

This flow may enable the formation of a resistance-based multi-layer or3D memory array with zero additional masking steps per memory layer,which utilizes junction-less transistors and has a resistance-basedmemory element in series with a select transistor, and is constructed bylayer transfers of wafer sized doped mono-crystalline silicon layers,and this 3D memory array may be connected to an underlying multi-metallayer semiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 101A through 101K are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the transistors may be ofanother type such as RCATs. Additionally, doping of each N+ layer may beslightly different to compensate for interconnect resistances. Moreover,the stacked memory layer may be connected to a periphery circuit that isabove the memory stack. Further, each gate of the double gate 3Dresistance based memory can be independently controlled for bettercontrol of the memory cell. Many other modifications within the scope ofthe invention will suggest themselves to such skilled persons afterreading this specification. Thus the invention is to be limited only bythe appended claims.

As illustrated in FIGS. 102A to 102L, a resistance-based 3D memory maybe constructed with zero additional masking steps per memory layer,which is suitable for 3D IC manufacturing. This 3D memory utilizesdouble gated MOSFET transistors and has a resistance-based memoryelement in series with a select transistor.

As illustrated in FIG. 102A, a silicon substrate with peripheralcircuitry 10202 may be constructed with high temperature (greater thanapproximately 400° C.) resistant wiring, such as, for example, Tungsten.The peripheral circuitry substrate 10202 may include memory controlcircuits as well as circuitry for other purposes and of various types,such as, for example, analog, digital, RF, or memory. The peripheralcircuitry substrate 10202 may include peripheral circuits that canwithstand an additional rapid-thermal-anneal (RTA) and still remainoperational and retain good performance. For this purpose, theperipheral circuits may be formed such that they have been subject to aweak RTA or no RTA for activating dopants. The top surface of theperipheral circuitry substrate 10202 may be prepared for oxide waferbonding with a deposition of a silicon oxide 10204, thus formingacceptor wafer 10214.

As illustrated in FIG. 102B, a mono-crystalline silicon donor wafer10212 may be optionally processed to comprise a wafer sized layer of P−doping (not shown) which may have a different dopant concentration thanthe P− substrate 10206. The P− doping layer may be formed by ionimplantation and thermal anneal. A screen oxide 10208 may be grown ordeposited prior to the implant to protect the silicon from implantcontamination and to provide an oxide surface for later wafer to waferbonding. A layer transfer demarcation plane 10210 (shown as a dashedline) may be formed in donor wafer 10212 within the P− substrate 10206or the P− doping layer (not shown) by hydrogen implantation or othermethods as previously described. Both the donor wafer 10212 and acceptorwafer 10214 may be prepared for wafer bonding as previously describedand then bonded at the surfaces of oxide layer 10204 and oxide layer10208, at a low temperature (less than approximately 400° C. preferredfor lowest stresses), or at a moderate temperature (less thanapproximately 900° C.).

As illustrated in FIG. 102C, the portion of the P− layer (not shown) andthe P− wafer substrate 10206 that are above the layer transferdemarcation plane 10210 may be removed by cleaving and polishing, orother processes as previously described, such as, for example, ion-cutor other methods, thus forming the remaining mono-crystalline silicon P−layer 10206′. Remaining P− layer 10206′ and oxide layer 10208 have beenlayer transferred to acceptor wafer 10214. The top surface of P− layer10206′ may be chemically or mechanically polished smooth and flat. Nowtransistors or portions of transistors may be formed and aligned to theacceptor wafer 10214 alignment marks (not shown). Oxide layer 10220 maybe deposited to prepare the surface for later oxide to oxide bonding.This now forms the first Si/SiO2 layer 10223 including silicon oxidelayer 10220, P− silicon layer 10206′, and oxide layer 10208.

As illustrated in FIG. 102D, additional Si/SiO2 layers, such as secondSi/SiO2 layer 10225 and third Si/SiO2 layer 10227, may each be formed asdescribed in FIGS. 102A to 102C. Oxide layer 10229 may be deposited toelectrically isolate the top silicon layer.

As illustrated in FIG. 102E, oxide 10229, third Si/SiO2 layer 10227,second Si/SiO2 layer 10225 and first Si/SiO2 layer 10223 may belithographically defined and plasma/RIE etched to form a portion of thememory cell structure, which now includes regions of P− silicon 10216and oxide 10222. Thus, these transistor elements or portions have beendefined by a common lithography step, which also may be described as asingle lithography step, same lithography step, or one lithography step.

As illustrated in FIG. 102F, a gate dielectric and gate electrodematerial may be deposited, planarized with a chemical mechanical polish(CMP), and then lithographically defined and plasma/RIE etched to formgate dielectric regions 10228 which may either be self-aligned to andcovered by gate electrodes 10230 (shown), or may cover the entiresilicon/oxide multi-layer structure. The gate stack including gateelectrode 10230 and gate dielectric 10228 may be formed with a gatedielectric, such as, for example, thermal oxide, and a gate electrodematerial, such as, for example, polycrystalline silicon. Alternatively,the gate dielectric may be an atomic layer deposited (ALD) material thatis paired with a work function specific gate metal according to anindustry standard of high k metal gate process schemes describedpreviously. Additionally, the gate dielectric may be formed with a rapidthermal oxidation (RTO), a low temperature oxide deposition or lowtemperature microwave plasma oxidation of the silicon surfaces and thena gate electrode such as tungsten or aluminum may be deposited.

As illustrated in FIG. 102G, N+ silicon regions 10226 may be formed in aself-aligned manner to the gate electrodes 10230 by ion implantation ofan N type species, such as, for example, Arsenic, into the regions of P−silicon 10216 that are not blocked by the gate electrodes 10230. Thisimplantation may also form the remaining regions of P− silicon 10217(not shown) in the gate electrode 10230 blocked areas. Different implantenergies or angles, or multiples of each, may be utilized to place the Ntype species into each layer of P− silicon regions 10216. Spacers (notshown) may be utilized during this multi-step implantation process andlayers of silicon present in different layers of the stack may havedifferent spacer widths to account for the differing lateral straggle ofN type species implants. Bottom layers, such as, for example, 10223,could have larger spacer widths than top layers, such as, for example,10227. Alternatively, angular ion implantation with substrate rotationmay be utilized to compensate for the differing implant straggle. Thetop layer implantation may have a slanted angle, rather thanperpendicular to the wafer surface, and hence land ions slightlyunderneath the gate electrode 10230 edges and closely match a moreperpendicular lower layer implantation which may land ions slightlyunderneath the gate electrode 10230 edge due to the straggle effects ofthe greater implant energy needed to reach the lower layer. A rapidthermal anneal (RTA) may be conducted to activate the dopants insubstantially all of the memory layers 10223, 10225, 10227 and in theperipheral circuits 10202. Alternatively, optical anneals, such as, forexample, a laser based anneal, may be performed.

As illustrated in FIG. 102H, the entire structure may be covered with agap fill oxide 10232, which may be planarized with chemical mechanicalpolishing. The oxide 10232 is shown transparent in the figure forclarity, along with word-line regions (WL) 10250, coupled with andcomposed of gate electrodes 10230, and source-line regions (SL) 10252,composed of indicated N+ silicon regions 10226.

As illustrated in FIG. 102I, bit-line (BL) contacts 10234 may belithographically defined, etched along with plasma/RIE through oxide10232, the three N+ silicon regions 10226, and associated oxide verticalisolation regions to connect substantially all memory layers vertically,and followed by photoresist removal. Resistance change memory material10238, such as hafnium oxide, may then be deposited, preferably withatomic layer deposition (ALD). The electrode for the resistance changememory element may then be deposited by ALD to form the electrode/BLcontact 10234. The excess deposited material may be polished toplanarity at or below the top of oxide 10232. Each BL contact 10234 withresistive change material 10238 may be shared among substantially alllayers of memory, shown as three layers of memory in FIG. 102I.

As illustrated in FIG. 102J, BL metal lines 10236 may be formed andconnect to the associated BL contacts 10234 with resistive changematerial 10238. Contacts and associated metal interconnect lines (notshown) may be formed for the WL and SL at the memory array edges. A thrulayer via 10260 (not shown) may be formed to electrically couple the BL,SL, and WL metallization to the acceptor substrate 10214 peripheralcircuitry via an acceptor wafer metal connect pad 10280 (not shown).

FIG. 102K1 is a cross-sectional cut II of FIG. 102K, while FIG. 102K2 isa cross-sectional cut III of FIG. 102K. FIG. 102K1 shows BL metal line10236, oxide 10232, BL contact/electrode 10234, resistive changematerial 10238, WL regions 10250, gate dielectric 10228, P− siliconregions 10217, N+ silicon regions 10226, and peripheral circuitssubstrate 10202. The BL contact/electrode 10234 couples to one side ofthe three levels of resistive change material 10238. The other side ofthe resistive change material 10238 is coupled to N+ silicon regions10226. FIG. 102K2 shows the P− regions 10217 with associated N+ regions10226 on each side form the source, channel, and drain of the selecttransistor. BL metal lines 10236, oxide 10232, gate electrode 10230,gate dielectric 10228, P− silicon regions 10217, interlayer oxideregions (‘ox’), and peripheral circuits substrate 10202. The gateelectrode 10230 is common to substantially all six P− silicon regions10217 and controls the six double gated MOSFET select transistors.

As illustrated in FIG. 102L, a single exemplary double gated MOSFETselect transistor on the first Si/SiO2 layer 10223 may include P−silicon region 10217 (functioning as the transistor channel), N+ siliconregions 10226 (functioning as source and drain), and two gate electrodes10230 with associated gate dielectrics 10228. The transistor iselectrically isolated from beneath by oxide layer 10208.

The above flow may enable the formation of a resistance-based 3D memorywith zero additional masking steps per memory layer constructed by layertransfers of wafer sized doped mono-crystalline silicon layers and maybe connected to an underlying multi-metal layer semiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 102A through 102L are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible, such as, for example, the transistors may be ofanother type such as RCATs. The MOSFET selectors may utilize lightlydoped drain and halo implants for channel engineering. Additionally, thecontacts may utilize doped poly-crystalline silicon, or other conductivematerials. Moreover, the stacked memory layer may be connected to aperiphery circuit that is above the memory stack. Further, each gate ofthe double gate 3D DRAM can be independently controlled for bettercontrol of the memory cell. Many other modifications within the scope ofthe invention will suggest themselves to such skilled persons afterreading this specification. Thus the invention is to be limited only bythe appended claims.

As illustrated in FIGS. 103A to 103M, a resistance-based 3D memory withone additional masking step per memory layer may be constructed that issuitable for 3D IC manufacturing. This 3D memory utilizes double gatedMOSFET select transistors and has a resistance-based memory element inseries with the select transistor.

As illustrated in FIG. 103A, a silicon substrate with peripheralcircuitry 10302 may be constructed with high temperature (greater thanapproximately 400° C.) resistant wiring, such as, for example, Tungsten.The peripheral circuitry substrate 10302 may include memory controlcircuits as well as circuitry for other purposes and of various types,such as, for example, analog, digital, RF, or memory. The peripheralcircuitry substrate 10302 may include circuits that can withstand anadditional rapid-thermal-anneal (RTA) and still remain operational andretain good performance. For this purpose, the peripheral circuits maybe formed such that they have been subject to a weak RTA or no RTA foractivating dopants. The top surface of the peripheral circuitrysubstrate 10302 may be prepared for oxide wafer bonding with adeposition of a silicon oxide 10304, thus forming acceptor wafer 2414.

As illustrated in FIG. 103B, a mono-crystalline silicon donor wafer10312 may be optionally processed to include a wafer sized layer of P−doping (not shown) which may have a different dopant concentration thanthe P− substrate 10306. The P− doping layer may be formed by ionimplantation and thermal anneal. A screen oxide 10308 may be grown ordeposited prior to the implant to protect the silicon from implantcontamination and to provide an oxide surface for later wafer to waferbonding. A layer transfer demarcation plane 10310 (shown as a dashedline) may be formed in donor wafer 10312 within the P− substrate 10306or the P− doping layer (not shown) by hydrogen implantation or othermethods as previously described. Both the donor wafer 10312 and acceptorwafer 10314 may be prepared for wafer bonding as previously describedand then bonded at the surfaces of oxide layer 10304 and oxide layer10308, at a low temperature (less than approximately 400° C. preferredfor lowest stresses), or a moderate temperature (less than approximately900° C.).

As illustrated in FIG. 103C, the portion of the P− layer (not shown) andthe P− wafer substrate 10306 that are above the layer transferdemarcation plane 10310 may be removed by cleaving and polishing, orother processes as previously described, such as ion-cut or othermethods, thus forming the remaining mono-crystalline silicon P− layer10306′. Remaining P− layer 10306′ and oxide layer 10308 have been layertransferred to acceptor wafer 10314. The top surface of P− layer 10306′may be chemically or mechanically polished smooth and flat. Nowtransistors or portions of transistors may be formed and aligned to theacceptor wafer 10314 alignment marks (not shown).

As illustrated in FIG. 103D, N+ silicon regions 10316 may belithographically defined and N type species, such as, for example,Arsenic, may be ion implanted into P− silicon layer 10306′. Thisimplantation also forms remaining regions of P− silicon 10318.

As illustrated in FIG. 103E, oxide layer 10320 may be deposited toprepare the surface for later oxide to oxide bonding, leading to theformation of the first Si/SiO2 layer 10323 including silicon oxide layer10320, N+ silicon regions 10316, and P− silicon regions 10318.

As illustrated in FIG. 103F, additional Si/SiO2 layers, such as, forexample. second Si/SiO2 layer 10325 and third Si/SiO2 layer 10327, mayeach be formed as described in FIGS. 103A to 103E. Oxide layer 10329 maybe deposited. After substantially all the numbers of memory layers areconstructed, a rapid thermal anneal (RTA) may be conducted to activatethe dopants in substantially all of the memory layers 10323, 10325,10327 and in the peripheral circuits 10302. Alternatively, opticalanneals, such as, for example, a laser based anneal, may be performed.

As illustrated in FIG. 103G, oxide layer 10329, third Si/SiO2 layer10327, second Si/SiO2 layer 10325 and first Si/SiO2 layer 10323 may belithographically defined and plasma/RIE etched to form a portion of thememory cell structure. The etching may result in regions of P− silicon10318′, which forms the transistor channels, and N+ silicon regions10316′, which form the source, drain and local source lines. Thus, thesetransistor elements or portions have been defined by a commonlithography step, which also may be described as a single lithographystep, same lithography step, or one lithography step.

As illustrated in FIG. 103H, a gate dielectric and gate electrodematerial may be deposited, planarized with a chemical mechanical polish(CMP), and then lithographically defined and plasma/RIE etched to formgate dielectric regions 10328 which may be either self-aligned to andcovered by gate electrodes 10330 (shown), or cover substantially theentire silicon/oxide multi-layer structure. The gate electrode 10330 andgate dielectric 10328 stack may be sized and aligned such that P−silicon regions 10318′ are substantially completely covered. The gatestack including gate electrode 10330 and gate dielectric 10328 may beformed with a gate dielectric, such as thermal oxide, and a gateelectrode material, such as, for example, poly-crystalline silicon.Alternatively, the gate dielectric may be an atomic layer deposited(ALD) material that is paired with a work function specific gate metalaccording to an industry standard of high k metal gate process schemesdescribed previously. Moreover, the gate dielectric may be formed with arapid thermal oxidation (RTO), a low temperature oxide deposition or lowtemperature microwave plasma oxidation of the silicon surfaces and thena gate electrode such as tungsten or aluminum may be deposited.

As illustrated in FIG. 103I, the entire structure may be covered with agap fill oxide 10332, which may be planarized with chemical mechanicalpolishing. The oxide 10332 is shown transparent in the figure forclarity, along with word-line regions (WL) 10350, coupled with andcomposed of gate electrodes 10330, and source-line regions (SL) 10352,composed of indicated N+ silicon regions 10316′.

As illustrated in FIG. 103J, bit-line (BL) contacts 10334 may belithographically defined, etched with plasma/RIE through oxide 10332,the three N+ silicon regions 10316′, and the associated oxide verticalisolation regions to connect substantially all memory layers vertically.BL contacts 10334 may then be processed by a photoresist removal.Resistance change memory material 10338, such as, for example, hafniumoxide, may then be deposited, preferably with atomic layer deposition(ALD). The electrode for the resistance change memory element may thenbe deposited by ALD to form the BL contact/electrode 10334. The excessdeposited material may be polished to planarity at or below the top ofoxide 10332. Each BL contact/electrode 10334 with resistive changematerial 10338 may be shared among substantially all layers of memory,shown as three layers of memory in FIG. 103J.

As illustrated in FIG. 103K, BL metal lines 10336 may be formed andconnected to the associated BL contacts 10334 with resistive changematerial 10338. Contacts and associated metal interconnect lines (notshown) may be formed for the WL and SL at the memory array edges. A thrulayer via 10360 (not shown) may be formed to electrically couple the BL,SL, and WL metallization to the acceptor substrate 10314 peripheralcircuitry via an acceptor wafer metal connect pad 10380 (not shown).

FIG. 103L1 is a cross section cut II view of FIG. 103L, while FIG. 103L2is a cross-sectional cut III view of FIG. 103L. FIG. 103L2 shows BLmetal line 10336, oxide 10332, BL contact/electrode 10334, resistivechange material 10338, WL regions 10350, gate dielectric 10328, P−silicon regions 10318′, N+ silicon regions 10316′, and peripheralcircuits substrate 10302. The BL contact/electrode 10334 couples to oneside of the three levels of resistive change material 10338. The otherside of the resistive change material 10338 is coupled to N+ siliconregions 10316′. The P− regions 10318′ with associated N+ regions 10316′on each side form the source, channel, and drain of the selecttransistor. FIG. 103L2 shows BL metal lines 10336, oxide 10332, gateelectrode 10330, gate dielectric 10328, P− silicon regions 10318′,interlayer oxide regions (‘ox’), and peripheral circuits substrate10302. The gate electrode 10330 is common to all six P− silicon regions10318′ and controls the six double gated MOSFET select transistors.

As illustrated in FIG. 103L, a single exemplary double gated MOSFETselect transistor on the first Si/SiO2 layer 10323 may include P−silicon region 10318′ (functioning as the transistor channel), N+silicon regions 10316′ (functioning as source and drain), and two gateelectrodes 10330 with associated gate dielectrics 10328. The transistoris electrically isolated from beneath by oxide layer 10308.

The above flow may enable the formation of a resistance-based 3D memorywith one additional masking step per memory layer constructed by layertransfers of wafer sized doped mono-crystalline silicon layers and maybe connected to an underlying multi-metal layer semiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 103A through 103M are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the transistors may be ofanother type, such as RCATs. Additionally, the contacts may utilizedoped poly-crystalline silicon, or other conductive materials. Moreover,the stacked memory layer may be connected to a periphery circuit that isabove the memory stack. Further, Si/SiO2 layers 10322, 10324 and 10326may be annealed layer-by-layer as soon as their associated implantationsare complete by using a laser anneal system. Many other modificationswithin the scope of the invention will suggest themselves to suchskilled persons after reading this specification. Thus the invention isto be limited only by the appended claims.

As illustrated in FIGS. 104A to 104F, a resistance-based 3D memory withtwo additional masking steps per memory layer may be constructed that issuitable for 3D IC manufacturing. This 3D memory utilizes single gateMOSFET select transistors and has a resistance-based memory element inseries with the select transistor.

As illustrated in FIG. 104A, a P− substrate donor wafer 10400 may beprocessed to include a wafer sized layer of P− doping 10404. The P−layer 10404 may have the same or different dopant concentration than theP− substrate 10400. The P− doping layer 10404 may be formed by ionimplantation and thermal anneal. A screen oxide 10401 may be grownbefore the implant to protect the silicon from implant contamination andto provide an oxide surface for later wafer to wafer bonding.

As illustrated in FIG. 104B, the top surface of donor wafer 10400 may beprepared for oxide wafer bonding with a deposition of an oxide 10402 orby thermal oxidation of the P− layer 10404 to form oxide layer 10402, ora re-oxidation of implant screen oxide 10401. A layer transferdemarcation plane 10499 (shown as a dashed line) may be formed in donorwafer 10400 or P− layer 10404 (shown) by hydrogen implantation 10407 orother methods as previously described. Both the donor wafer 10400 andacceptor wafer 10410 may be prepared for wafer bonding as previouslydescribed and then bonded, preferably at a low temperature (less thanapproximately 400° C.) to minimize stresses. The portion of the P− layer10404 and the P− donor wafer substrate 10400 above the layer transferdemarcation plane 10499 may be removed by cleaving and polishing, orother processes as previously described, such as, for example, ion-cutor other methods.

As illustrated in FIG. 104C, the remaining P− doped layer 10404′, andoxide layer 10402 have been layer transferred to acceptor wafer 10410.Acceptor wafer 10410 may include peripheral circuits such that they canwithstand an additional rapid-thermal-anneal (RTA) and still remainoperational and retain good performance. For this purpose, theperipheral circuits may be formed such that they have been subject to aweak RTA or no RTA for activating dopants. Also, the peripheral circuitsmay utilize a refractory metal such as tungsten that can withstand hightemperatures greater than approximately 400° C. The top surface of P−doped layer 10404′ may be chemically or mechanically polished smooth andflat. Now transistors may be formed and aligned to the acceptor wafer10410 alignment marks (not shown).

As illustrated in FIG. 104D, shallow trench isolation (STI) oxideregions (not shown) may be lithographically defined and plasma/RIEetched to at least the top level of oxide layer 10402, thus removingregions of P− mono-crystalline silicon layer 10404′. A gap-fill oxidemay be deposited and CMP'ed flat to form conventional STI oxide regionsand P− doped mono-crystalline silicon regions (not shown) for formingthe transistors. Threshold adjust implants may or may not be performedat this time. A gate stack 10424 may be formed with a gate dielectric,such as, for example, thermal oxide, and a gate metal material, such as,for example, polycrystalline silicon. Alternatively, the gate oxide maybe an atomic layer deposited (ALD) gate dielectric that is paired with awork function specific gate metal according to an industry standard ofhigh k metal gate process schemes described previously. Moreover, thegate oxide may be formed with a rapid thermal oxidation (RTO), a lowtemperature oxide deposition or low temperature microwave plasmaoxidation of the silicon surfaces and then a gate material such as, forexample, tungsten or aluminum may be deposited. Gate stack self-alignedLDD (Lightly Doped Drain) and halo punch-thru implants may be performedat this time to adjust junction and transistor breakdowncharacteristics. A conventional spacer deposition of oxide and nitrideand a subsequent etch-back may be done to form implant offset spacers(not shown) on the gate stacks 10424. Then a self-aligned N+ source anddrain implant may be performed to create transistor source and drains10420 and remaining P− silicon NMOS transistor channels 10428. Hightemperature anneal steps may or may not be done at this time to activatethe implants and set initial junction depths. Finally, the entirestructure may be covered with a gap fill oxide 10450, which may beplanarized with chemical mechanical polishing. The oxide surface may beprepared for oxide to oxide wafer bonding as previously described.

As illustrated in FIG. 104E, the transistor layer formation, bonding toacceptor wafer 10410 oxide 10450, and subsequent transistor formation asdescribed in FIGS. 104A to 104D may be repeated to form the second tier10430 of memory transistors. After substantially all the memory layersare constructed, a rapid thermal anneal (RTA) may be conducted toactivate the dopants in substantially all of the memory layers and inthe acceptor substrate 10410 peripheral circuits. Alternatively, opticalanneals, such as, for example, a laser based anneal, may be performed.

As illustrated in FIG. 104F, contacts and metal interconnects may beformed by lithography and plasma/RIE etch. Bit line (BL) contacts 10440electrically couple the memory layers' transistor N+ regions on thetransistor drain side 10454, and the source line contact 10442electrically couples the memory layers' transistor N+ regions on thetransistors source side 10452. The bit-line (BL) wiring 10448 andsource-line (SL) wiring 10446 electrically couples the bit-line contacts10440 and source-line contacts 10442 respectively. The gate stacks, suchas 10434, may be connected with a contact and metallization (not shown)to form the word-lines (WLs). A thru layer via 10460 (not shown) may beformed to electrically couple the BL, SL, and WL metallization to theacceptor substrate 10410 peripheral circuitry via an acceptor wafermetal connect pad 1980 (not shown).

As illustrated in FIG. 104F, source-line (SL) contacts 10434 may belithographically defined, etched with plasma/RIE through the oxide 10450and N+ silicon regions 10420 of each memory tier, and the associatedoxide vertical isolation regions to connect substantially all memorylayers vertically. SL contacts may then be processed by a photoresistremoval. Resistance change memory material 10442, such as, for example,hafnium oxide, may then be deposited, preferably with atomic layerdeposition (ALD). The electrode for the resistance change memory elementmay then be deposited by ALD to form the SL contact/electrode 10434. Theexcess deposited material may be polished to planarity at or below thetop of oxide 10450. Each SL contact/electrode 10434 with resistivechange material 10442 may be shared among substantially all layers ofmemory, shown as two layers of memory in FIG. 104F. The SL contact 10434electrically couples the memory layers' transistor N+ regions on thetransistor source side 10452. SL metal lines 10446 may be formed andconnected to the associated SL contacts 10434 with resistive changematerial 10442. Oxide layer 10452 may be deposited and planarized.Bit-line (BL) contacts 10440 may be lithographically defined, etchedalong with plasma/RIE through oxide 10452, the oxide 10450 and N+silicon regions 10420 of each memory tier, and the associated oxidevertical isolation regions to connect substantially all memory layersvertically. BL contacts 10440 may then be processed by a photoresistremoval. BL contacts 10440 electrically couple the memory layers'transistor N+ regions on the transistor drain side 10454. BL metal lines10448 may be formed and connect to the associated BL contacts 10440. Thegate stacks, such as 10424, may be connected with a contact andmetallization (not shown) to form the word-lines (WLs). A thru layer via10460 (not shown) may be formed to electrically couple the BL, SL, andWL metallization to the acceptor substrate 10410 peripheral circuitryvia an acceptor wafer metal connect pad 10480 (not shown).

This flow may enable the formation of a resistance-based 3D memory withtwo additional masking steps per memory layer constructed by layertransfers of wafer sized doped layers and this 3D memory may beconnected to an underlying multi-metal layer semiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 104A through 104F are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the transistors may be ofanother type such as PMOS or RCATs. Additionally, the stacked memorylayer may be connected to a periphery circuit that is above the memorystack. Moreover, each tier of memory could be configured with a slightlydifferent donor wafer P− layer doping profile. Further, the memory couldbe organized in a different manner, such as BL and SL interchanged, orwhere there are buried wiring whereby wiring for the memory array isbelow the memory layers but above the periphery. Many othermodifications within the scope of the invention will suggest themselvesto such skilled persons after reading this specification. Thus theinvention is to be limited only by the appended claims.

Charge trap NAND (Negated AND) memory devices are another form ofpopular commercial non-volatile memories. Charge trap device store theircharge in a charge trap layer, wherein this charge trap layer theninfluences the channel of a transistor. Background information oncharge-trap memory can be found in “Integrated Interconnect Technologiesfor 3D Nanoelectronic Systems”, Artech House, 2009 by Bakir and Meindl(hereinafter Bakir), “A Highly Scalable 8-Layer 3D Vertical-Gate (VG)TFT NAND Flash Using Junction-Free Buried Channel BE-SONOS Device,”Symposium on VLSI Technology, 2010 by Hang-Ting Lue, et al. and“Introduction to Flash memory,” Proc. IEEE 91, 489-502 (2003) by R. Bez,et al. Work described in Bakir utilized selective epitaxy, laserrecrystallization, or polysilicon to form the transistor channel, whichresults in less than satisfactory transistor performance. Thearchitectures shown in FIGS. 105 and 106 are relevant for any type ofcharge-trap memory.

As illustrated in FIGS. 105A to 105G, a charge trap based two additionalmasking steps per memory layer 3D memory may be constructed that issuitable for 3D IC. This 3D memory utilizes NAND strings of charge traptransistors constructed in mono-crystalline silicon.

As illustrated in FIG. 105A, a P− substrate donor wafer 10500 may beprocessed to include a wafer sized layer of P− doping 10504. The P-dopedlayer 10504 may have the same or different dopant concentration than theP− substrate 10500. The P− doped layer 10504 may have a vertical dopantgradient. The P− doped layer 10504 may be formed by ion implantation andthermal anneal. A screen oxide 10501 may be grown before the implant toprotect the silicon from implant contamination and to provide an oxidesurface for later wafer to wafer bonding.

As illustrated in FIG. 105B, the top surface of donor wafer 10500 may beprepared for oxide wafer bonding with a deposition of an oxide 10502 orby thermal oxidation of the P− doped layer 10504 to form oxide layer10502, or a re-oxidation of implant screen oxide 10501. A layer transferdemarcation plane 10599 (shown as a dashed line) may be formed in donorwafer 10500 or P− layer 10504 (shown) by hydrogen implantation 10507 orother methods as previously described. Both the donor wafer 10500 andacceptor wafer 10510 may be prepared for wafer bonding as previouslydescribed and then bonded, preferably at a low temperature (e.g., lessthan approximately 400° C.) to minimize stresses. The portion of the P−layer 10504 and the P− donor wafer substrate 10500 that are above thelayer transfer demarcation plane 10599 may be removed by cleaving andpolishing, or other processes as previously described, such as ion-cutor other methods.

As illustrated in FIG. 105C, the remaining P− doped layer 10504′, andoxide layer 10502 have been layer transferred to acceptor wafer 10510.Acceptor wafer 10510 may include peripheral circuits such that theaccepter wafer can withstand an additional rapid-thermal-anneal (RTA)and still remain operational and retain good performance. For thispurpose, the peripheral circuits may be formed such that they have beensubject to a weak RTA or no RTA for activating dopants. Also, theperipheral circuits may utilize a refractory metal such as, for example,tungsten that can withstand high temperatures greater than approximately400° C. The top surface of P− doped layer 10504′ may be chemically ormechanically polished smooth and flat. Now transistors may be formed andaligned to the acceptor wafer 10510 alignment marks (not shown).

As illustrated in FIG. 105D, shallow trench isolation (STI) oxideregions (not shown) may be lithographically defined and plasma/RIEetched to at least the top level of oxide layer 10502, thus removingregions of P− mono-crystalline silicon layer 10504′ and forming P− dopedregions 10520. A gap-fill oxide may be deposited and CMP'ed flat to formconventional STI oxide regions and P− doped mono-crystalline siliconregions (not shown) for forming the transistors. Threshold adjustimplants may or may not be performed at this time. A gate stack may beformed with growth or deposition of a charge trap gate dielectric 10522,such as, for example, thermal oxide and silicon nitride layers (ONO:Oxide-Nitride-Oxide), and a gate metal material 10524, such as, forexample, doped or undoped poly-crystalline silicon. Alternatively, thecharge trap gate dielectric may comprise silicon or III-V nano-crystalsencased in an oxide.

As illustrated in FIG. 105E, gate stacks 10528 may be lithographicallydefined and plasma/RIE etched, thus removing regions of gate metalmaterial 10524 and charge trap gate dielectric 10522. A self-aligned N+source and drain implant may be performed to create inter-transistorsource and drains 10534 and end of NAND string source and drains 10530.Finally, the entire structure may be covered with a gap fill oxide 10550and the oxide planarized with chemical mechanical polishing. The oxidesurface may be prepared for oxide to oxide wafer bonding as previouslydescribed. This now forms the first tier of memory transistors 10542including silicon oxide layer 10550, gate stacks 10528, inter-transistorsource and drains 10534, end of NAND string source and drains 10530, P−silicon regions 10520, and oxide 10502.

As illustrated in FIG. 105F, the transistor layer formation, bonding toacceptor wafer 10510 oxide 10550, and subsequent transistor formation asdescribed in FIGS. 105A to 105D may be repeated to form the second tier10544 of memory transistors on top of the first tier of memorytransistors 10542. After substantially all the memory layers areconstructed, a rapid thermal anneal (RTA) may be conducted to activatethe dopants in substantially all of the memory layers and in theacceptor substrate 10510 peripheral circuits. Alternatively, opticalanneals, such as, for example, a laser based anneal, may be performed.

As illustrated in FIG. 105G, source line (SL) ground contact 10548 andbit line contact 10549 may be lithographically defined, etched alongwith plasma/RIE through oxide 10550, end of NAND string source anddrains 10530, P− regions 10520 of each memory tier, and the associatedoxide vertical isolation regions to connect substantially all memorylayers vertically. SL ground contacts and bit line contact may then beprocessed by a photoresist removal. Metal or heavily dopedpoly-crystalline silicon may be utilized to fill the contacts andmetallization utilized to form BL and SL wiring (not shown). The gatestacks 10528 may be connected with a contact and metallization to formthe word-lines (WLs) and WL wiring (not shown). A thru layer via 10560(not shown) may be formed to electrically couple the BL, SL, and WLmetallization to the acceptor substrate 10510 peripheral circuitry viaan acceptor wafer metal connect pad 10580 (not shown).

This flow may enable the formation of a charge trap based 3D memory withtwo additional masking steps per memory layer constructed by layertransfers of wafer sized doped layers of mono-crystalline silicon andthis 3D memory may be connected to an underlying multi-metal layersemiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 105A through 105G are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, BL or SL selecttransistors may be constructed within the process flow. Moreover, thestacked memory layer may be connected to a periphery circuit that isabove the memory stack. Additionally, each tier of memory could beconfigured with a slightly different donor wafer P− layer dopingprofile. Further, the memory could be organized in a different manner,such as BL and SL interchanged, or these architectures can be modifiedinto a NOR flash memory style, or where buried wiring for the memoryarray is below the memory layers but above the periphery. Besides, thecharge trap dielectric and gate layer may be deposited before the layertransfer and temporarily bonded to a carrier or holder wafer orsubstrate and then transferred to the acceptor substrate with periphery.Many other modifications within the scope of the invention will suggestthemselves to such skilled persons after reading this specification.Thus the invention is to be limited only by the appended claims.

As illustrated in FIGS. 106A to 106G, a charge trap based 3D memory withzero additional masking steps per memory layer 3D memory may beconstructed that is suitable for 3D IC manufacturing. This 3D memoryutilizes NAND strings of charge trap junction-less transistors withjunction-less select transistors constructed in mono-crystallinesilicon.

As illustrated in FIG. 106A, a silicon substrate with peripheralcircuitry 10602 may be constructed with high temperature (e.g., greaterthan approximately 400° C.) resistant wiring, such as, for example,Tungsten. The peripheral circuitry substrate 10602 may include memorycontrol circuits as well as circuitry for other purposes and of varioustypes, such as, for example, analog, digital, RF, or memory. Theperipheral circuitry substrate 10602 may include peripheral circuitsthat can withstand an additional rapid-thermal-anneal (RTA) and stillremain operational and retain good performance. For this purpose, theperipheral circuits may be formed such that they have been subject to aweak RTA or no RTA for activating dopants. The top surface of theperipheral circuitry substrate 10602 may be prepared for oxide waferbonding with a deposition of a silicon oxide 10604, thus formingacceptor wafer 10614.

As illustrated in FIG. 106B, a mono-crystalline silicon donor wafer10612 may be processed to include a wafer sized layer of N+ doping (notshown) which may have a different dopant concentration than the N+substrate 10606. The N+ doping layer may be formed by ion implantationand thermal anneal. A screen oxide 10608 may be grown or deposited priorto the implant to protect the silicon from implant contamination and toprovide an oxide surface for later wafer to wafer bonding. A layertransfer demarcation plane 10610 (shown as a dashed line) may be formedin donor wafer 10612 within the N+ substrate 10606 or the N+ dopinglayer (not shown) by hydrogen implantation or other methods aspreviously described. Both the donor wafer 10612 and acceptor wafer10614 may be prepared for wafer bonding as previously described and thenbonded at the surfaces of oxide layer 10604 and oxide layer 10608, at alow temperature (e.g., less than approximately 400° C. preferred forlowest stresses), or a moderate temperature (e.g., less thanapproximately 900° C.).

As illustrated in FIG. 106C, the portion of the N+ layer (not shown) andthe N+ wafer substrate 10606 that are above the layer transferdemarcation plane 10610 may be removed by cleaving and polishing, orother processes as previously described, such as ion-cut or othermethods, thus forming the remaining mono-crystalline silicon N+ layer10606′. Remaining N+ layer 10606′ and oxide layer 10608 have been layertransferred to acceptor wafer 10614. The top surface of N+ layer 10606′may be chemically or mechanically polished smooth and flat. Oxide layer10620 may be deposited to prepare the surface for later oxide to oxidebonding. This now forms the first Si/SiO2 layer 10623 comprised ofsilicon oxide layer 10620, N+ silicon layer 10606′, and oxide layer10608.

As illustrated in FIG. 106D, additional Si/SiO2 layers, such as, forexample, second Si/SiO2 layer 10625 and third Si/SiO2 layer 10627, mayeach be formed as described in FIGS. 106A to 106C. Oxide layer 10629 maybe deposited to electrically isolate the top N+ silicon layer.

As illustrated in FIG. 106E, oxide 10629, third Si/SiO2 layer 10627,second Si/SiO2 layer 10625 and first Si/SiO2 layer 10623 may belithographically defined and plasma/RIE etched to form a portion of thememory cell structure, which now includes regions of N+ silicon 10626and oxide 10622. Thus, these transistor elements or portions have beendefined by a common lithography step, which also may be described as asingle lithography step, same lithography step, or one lithography step.

As illustrated in FIG. 106F, a gate stack may be formed with growth ordeposition of a charge trap gate dielectric layer, such as thermal oxideand silicon nitride layers (ONO: Oxide-Nitride-Oxide), and a gate metalelectrode layer, such as doped or undoped poly-crystalline silicon. Thegate metal electrode layer may then be planarized with chemicalmechanical polishing. Alternatively, the charge trap gate dielectriclayer may comprise silicon or III-V nano-crystals encased in an oxide.The select gate area 10638 may comprise a non-charge trap dielectric.The gate metal electrode regions 10630 and gate dielectric regions 10628of both the NAND string area 10636 and select transistor area 10638 maybe lithographically defined and plasma/RIE etched.

As illustrated in FIG. 106G, the entire structure may be covered with agap fill oxide 10632, which may be planarized with chemical mechanicalpolishing. The oxide 10632 is shown transparent in the figure forclarity. Select metal lines 10646 may be formed and connected to theassociated select gate contacts 10634. Contacts and associated metalinterconnect lines (not shown) may be formed for the WL and SL at thememory array edges. Word-line regions (WL) 10636, gate electrodes 10630,and bit-line regions (BL) 10652 including indicated N+ silicon regions10626, are shown. Source regions 10644 may be formed by trench contactetch and fill to couple to the N+ silicon regions on the source end ofthe NAND string 10636. A thru layer via 10660 (not shown) may be formedto electrically couple the BL, SL, and WL metallization to the acceptorsubstrate 10614 peripheral circuitry via an acceptor wafer metal connectpad 10680 (not shown).

This flow may enable the formation of a charge trap based 3D memory withzero additional masking steps per memory layer constructed by layertransfers of wafer sized doped layers of mono-crystalline silicon andthis 3D memory may be connected to an underlying multi-metal layersemiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 106A through 106G are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, BL or SL contacts may beconstructed in a staircase manner as described previously. Moreover, thestacked memory layer may be connected to a periphery circuit that isabove the memory stack. Additionally, each tier of memory could beconfigured with a slightly different donor wafer N+ layer dopingprofile. Further, the memory could be organized in a different manner,such as BL and SL interchanged, or where buried wiring for the memoryarray is below the memory layers but above the periphery. Additionaltypes of 3D charge trap memories may be constructed by layer transfer ofmono-crystalline silicon; for example, those found in “A Highly Scalable8-Layer 3D Vertical-Gate (VG) TFT NAND Flash Using Junction-Free BuriedChannel BE-SONOS Device,” Symposium on VLSI Technology, 2010 byHang-Ting Lue, et al., and “Multi-layered Vertical Gate NAND Flashovercoming stacking limit for terabit density storage”, Symposium onVLSI Technology, 2009 by W. Kim, S. Choi, et al. Many othermodifications within the scope of the invention will suggest themselvesto such skilled persons after reading this specification. Thus theinvention is to be limited only by the appended claims.

Floating gate (FG) memory devices are another form of popular commercialnon-volatile memories. Floating gate devices store their charge in aconductive gate (FG) that is nominally isolated from unintentionalelectric fields, wherein the charge on the FG then influences thechannel of a transistor. Background information on floating gate flashmemory can be found in “Introduction to Flash memory”, Proc. IEEE 91,489-502 (2003) by R. Bez, et al. The architectures shown in FIGS. 107and 108 are relevant for any type of floating gate memory.

As illustrated in FIGS. 107A to 107G, a floating gate based 3D memorywith two additional masking steps per memory layer may be constructedthat is suitable for 3D IC manufacturing. This 3D memory utilizes NANDstrings of floating gate transistors constructed in mono-crystallinesilicon.

As illustrated in FIG. 107A, a P− substrate donor wafer 10700 may beprocessed to include a wafer sized layer of P− doping 10704. The P-dopedlayer 10704 may have the same or a different dopant concentration thanthe P− substrate 10700. The P− doped layer 10704 may have a verticaldopant gradient. The P− doped layer 10704 may be formed by ionimplantation and thermal anneal. A screen oxide 10701 may be grownbefore the implant to protect the silicon from implant contamination andto provide an oxide surface for later wafer to wafer bonding.

As illustrated in FIG. 107B, the top surface of donor wafer 10700 may beprepared for oxide wafer bonding with a deposition of an oxide 10702 orby thermal oxidation of the P− doped layer 10704 to form oxide layer10702, or a re-oxidation of implant screen oxide 10701. A layer transferdemarcation plane 10799 (shown as a dashed line) may be formed in donorwafer 10700 or P− layer 10704 (shown) by hydrogen implantation 10707 orother methods as previously described. Both the donor wafer 10700 andacceptor wafer 10710 may be prepared for wafer bonding as previouslydescribed and then bonded, preferably at a low temperature (less thanapproximately 400° C.) to minimize stresses. The portion of the P− layer10704 and the P− donor wafer substrate 10700 that are above the layertransfer demarcation plane 10799 may be removed by cleaving andpolishing, or other processes as previously described, such as ion-cutor other methods.

As illustrated in FIG. 107C, the remaining P− doped layer 10704′, andoxide layer 10702 have been layer transferred to acceptor wafer 10710.Acceptor wafer 10710 may include peripheral circuits such that they canwithstand an additional rapid-thermal-anneal (RTA) and still remainoperational and retain good performance. For this purpose, theperipheral circuits may be formed such that they have been subject to aweak RTA or no RTA for activating dopants. Also, the peripheral circuitsmay utilize a refractory metal such as, for example, tungsten that canwithstand high temperatures greater than approximately 400° C. The topsurface of P− doped layer 10704′ may be chemically or mechanicallypolished smooth and flat. Now transistors may be formed and aligned tothe acceptor wafer 10710 alignment marks (not shown).

As illustrated in FIG. 107D a partial gate stack may be formed withgrowth or deposition of a tunnel oxide 10722, such as, for example,thermal oxide, and a FG gate metal material 10724, such as, for example,doped or undoped poly-crystalline silicon. Shallow trench isolation(STI) oxide regions (not shown) may be lithographically defined andplasma/RIE etched to at least the top level of oxide layer 10702, thusremoving regions of P− mono-crystalline silicon layer 10704′ and formingP− doped regions 10720. A gap-fill oxide may be deposited and CMP'edflat to form conventional STI oxide regions (not shown).

As illustrated in FIG. 107E, an inter-poly oxide layer 10725, such assilicon oxide and silicon nitride layers (ONO: Oxide-Nitride-Oxide), anda Control Gate (CG) gate metal material 10726, such as doped or undopedpoly-crystalline silicon, may be deposited. The gate stacks 10728 may belithographically defined and plasma/RIE etched, thus removing regions ofCG gate metal material 10726, inter-poly oxide layer 10725, FG gatemetal material 10724, and tunnel oxide 10722. This removal may result inthe gate stacks 10728 including CG gate metal regions 10726′, inter-polyoxide regions 10725′, FG gate metal regions 10724, and tunnel oxideregions 10722′. Only one gate stack 10728 is annotated with region tielines for clarity. A self-aligned N+ source and drain implant may beperformed to create inter-transistor source and drains 10734 and end ofNAND string source and drains 10730. Finally, the entire structure maybe covered with a gap fill oxide 10750, which may be planarized withchemical mechanical polishing. The oxide surface may be prepared foroxide to oxide wafer bonding as previously described. This now forms thefirst tier of memory transistors 10742 including silicon oxide layer10750, gate stacks 10728, inter-transistor source and drains 10734, endof NAND string source and drains 10730, P− silicon regions 10720, andoxide 10702.

As illustrated in FIG. 107F, the transistor layer formation, bonding toacceptor wafer 10710 oxide 10750, and subsequent transistor formation asdescribed in FIGS. 107A to 107D may be repeated to form the second tier10744 of memory transistors on top of the first tier of memorytransistors 10742. After substantially all the memory layers areconstructed, a rapid thermal anneal (RTA) may be conducted to activatethe dopants in substantially all of the memory layers and in theacceptor substrate 10710 peripheral circuits. Alternatively, opticalanneals, such as, for example, a laser based anneal, may be performed.

As illustrated in FIG. 107G, source line (SL) ground contact 10748 andbit line contact 10749 may be lithographically defined, etched withplasma/RIE through oxide 10750, end of NAND string source and drains10730, and P− regions 10720 of each memory tier, and the associatedoxide vertical isolation regions to connect substantially all memorylayers vertically. SL ground contact 10748 and bit line contact 10749may then be processed by a photoresist removal. Metal or heavily dopedpoly-crystalline silicon may be utilized to fill the contacts andmetallization utilized to form BL and SL wiring (not shown). The gatestacks 10728 may be connected with a contact and metallization to formthe word-lines (WLs) and WL wiring (not shown). A thru layer via 10760(not shown) may be formed to electrically couple the BL, SL, and WLmetallization to the acceptor substrate 10710 peripheral circuitry viaan acceptor wafer metal connect pad 10780 (not shown).

This flow may enable the formation of a floating gate based 3D memorywith two additional masking steps per memory layer constructed by layertransfers of wafer sized doped layers of mono-crystalline silicon andthis 3D memory may be connected to an underlying multi-metal layersemiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 107A through 107G are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, BL or SL selecttransistors may be constructed within the process flow. Moreover, thestacked memory layer may be connected to a periphery circuit that isabove the memory stack. Additionally, each tier of memory could beconfigured with a slightly different donor wafer P− layer dopingprofile. Further, the memory could be organized in a different manner,such as BL and SL interchanged, or where buried wiring for the memoryarray is below the memory layers but above the periphery. Many othermodifications within the scope of the invention will suggest themselvesto such skilled persons after reading this specification. Thus theinvention is to be limited only by the appended claims.

As illustrated in FIGS. 108A to 108H, a floating gate based 3D memorywith one additional masking step per memory layer 3D memory may beconstructed that is suitable for 3D IC manufacturing. This 3D memoryutilizes 3D floating gate junction-less transistors constructed inmono-crystalline silicon.

As illustrated in FIG. 108A, a silicon substrate with peripheralcircuitry 10802 may be constructed with high temperature (greater thanapproximately 400° C.) resistant wiring, such as, for example, Tungsten.The peripheral circuitry substrate 10802 may include memory controlcircuits as well as circuitry for other purposes and of various types,such as, for example, analog, digital, RF, or memory. The peripheralcircuitry substrate 10802 may include peripheral circuits that canwithstand an additional rapid-thermal-anneal (RTA) and still remainoperational and retain good performance. For this purpose, theperipheral circuits may be formed such that they have been subject to aweak RTA or no RTA for activating dopants. The top surface of theperipheral circuitry substrate 10802 may be prepared for oxide waferbonding with a deposition of a silicon oxide 10804, thus formingacceptor wafer 10814.

As illustrated in FIG. 108B, a mono-crystalline N+ doped silicon donorwafer 10812 may be processed to include a wafer sized layer of N+ doping(not shown) which may have a different dopant concentration than the N+substrate 10806. The N+ doping layer may be formed by ion implantationand thermal anneal. A screen oxide 10808 may be grown or deposited priorto the implant to protect the silicon from implant contamination and toprovide an oxide surface for later wafer to wafer bonding. A layertransfer demarcation plane 10810 (shown as a dashed line) may be formedin donor wafer 10812 within the N+ substrate 10806 or the N+ dopinglayer (not shown) by hydrogen implantation or other methods aspreviously described. Both the donor wafer 10812 and acceptor wafer10814 may be prepared for wafer bonding as previously described and thenbonded at the surfaces of oxide layer 10804 and oxide layer 10808, at alow temperature (e.g., less than approximately 400° C. preferred forlowest stresses), or a moderate temperature (e.g., less thanapproximately 900° C.).

As illustrated in FIG. 108C, the portion of the N+ layer (not shown) andthe N+ wafer substrate 10806 that are above the layer transferdemarcation plane 10810 may be removed by cleaving and polishing, orother processes as previously described, such as ion-cut or othermethods, thus forming the remaining mono-crystalline silicon N+ layer10806′. Remaining N+ layer 10806′ and oxide layer 10808 have been layertransferred to acceptor wafer 10814. The top surface of N+ layer 10806′may be chemically or mechanically polished smooth and flat. Nowtransistors or portions of transistors may be formed and aligned to theacceptor wafer 10814 alignment marks (not shown).

As illustrated in FIG. 108D N+ regions 10816 may be lithographicallydefined and then etched with plasma/RIE, thus removing regions of N+layer 10806′ and stopping on or partially within oxide layer 10808.

As illustrated in FIG. 108E, a tunneling dielectric 10818 may be grownor deposited, such as thermal silicon oxide, and a floating gate (FG)material 10828, such as doped or undoped poly-crystalline silicon, maybe deposited. The structure may be planarized by chemical mechanicalpolishing to approximately the level of the N+ regions 10816. Thesurface may be prepared for oxide to oxide wafer bonding as previouslydescribed, such as a deposition of a thin oxide. This now forms thefirst memory layer 10823 including future FG regions 10828, tunnelingdielectric 10818, N+ regions 10816 and oxide 10808.

As illustrated in FIG. 108F, the N+ layer formation, bonding to anacceptor wafer, and subsequent memory layer formation as described inFIGS. 108A to 108E may be repeated to form the second layer 10825 ofmemory on top of the first memory layer 10823. A layer of oxide 10829may then be deposited.

As illustrated in FIG. 108G, FG regions 10838 may be lithographicallydefined and then etched along with plasma/RIE removing portions of oxidelayer 10829, future FG regions 10828 and oxide layer 10808 on the secondlayer of memory 10825 and future FG regions 10828 on the first layer ofmemory 10823, thus stopping on or partially within oxide layer 10808 ofthe first memory layer 10823.

As illustrated in FIG. 108H, an inter-poly oxide layer 10850, such as,for example, silicon oxide and silicon nitride layers (ONO:Oxide-Nitride-Oxide), and a Control Gate (CG) gate material 10852, suchas, for example, doped or undoped poly-crystalline silicon, may bedeposited. The surface may be planarized by chemical mechanicalpolishing leaving a thinned oxide layer 10829′. As shown in theillustration, this results in the formation of 4 horizontally orientedfloating gate memory bit cells with N+ junction-less transistors.Contacts and metal wiring to form well-know memory access/decodingschemes may be processed and a thru layer via (TLV) may be formed toelectrically couple the memory access decoding to the acceptor substrateperipheral circuitry via an acceptor wafer metal connect pad.

This flow may enable the formation of a floating gate based 3D memorywith one additional masking step per memory layer constructed by layertransfers of wafer sized doped layers of mono-crystalline silicon andthis 3D memory may be connected to an underlying multi-metal layersemiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 108A through 108H are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, memory cell control linescould be built in a different layer rather than the same layer.Moreover, the stacked memory layers may be connected to a peripherycircuit that is above the memory stack. Additionally, each tier ofmemory could be configured with a slightly different donor wafer N+layer doping profile. Further, the memory could be organized in adifferent manner, such as BL and SL interchanged, or these architecturescould be modified into a NOR flash memory style, or where buried wiringfor the memory array is below the memory layers but above the periphery.Many other modifications within the scope of the invention will suggestthemselves to such skilled persons after reading this specification.

The monolithic 3D integration concepts described in this patentapplication can lead to novel embodiments of poly-crystalline siliconbased memory architectures. While the below concepts in FIGS. 109 and110 are explained by using resistive memory architectures as an example,it will be clear to one skilled in the art that similar concepts can beapplied to the NAND flash, charge trap, and DRAM memory architecturesand process flows described previously in this patent application.

As illustrated in FIGS. 109A to 109K, a resistance-based 3D memory withzero additional masking steps per memory layer may be constructed withmethods that are suitable for 3D IC manufacturing. This 3D memoryutilizes poly-crystalline silicon junction-less transistors that mayhave either a positive or a negative threshold voltage and has aresistance-based memory element in series with a select or accesstransistor.

As illustrated in FIG. 109A, a silicon substrate with peripheralcircuitry 10902 may be constructed with high temperature (greater thanapproximately 400° C.) resistant wiring, such as, for example, Tungsten.The peripheral circuitry substrate 10902 may include memory controlcircuits as well as circuitry for other purposes and of various types,such as, for example, analog, digital, RF, or memory. The peripheralcircuitry substrate 10902 may include peripheral circuits that canwithstand an additional rapid-thermal-anneal (RTA) and still remainoperational and retain good performance. For this purpose, theperipheral circuits may be formed such that they have been subject to apartial or weak RTA or no RTA for activating dopants. Silicon oxidelayer 10904 is deposited on the top surface of the peripheral circuitrysubstrate.

As illustrated in FIG. 109B, a layer of N+ doped poly-crystalline oramorphous silicon 10906 may be deposited. The amorphous silicon orpoly-crystalline silicon layer 10906 may be deposited using a chemicalvapor deposition process, such as LPCVD or PECVD, or other processmethods, and may be deposited doped with N+ dopants, such as Arsenic orPhosphorous, or may be deposited un-doped and subsequently doped with,such as, ion implantation or PLAD (PLasma Assisted Doping) techniques.Silicon Oxide 10920 may then be deposited or grown. This now forms thefirst Si/SiO2 layer 10923 which includes N+ doped poly-crystalline oramorphous silicon layer 10906 and silicon oxide layer 10920.

As illustrated in FIG. 109C, additional Si/SiO2 layers, such as, forexample, second Si/SiO2 layer 10925 and third Si/SiO2 layer 10927, mayeach be formed as described in FIG. 109B. Oxide layer 10929 may bedeposited to electrically isolate the top N+ doped poly-crystalline oramorphous silicon layer.

As illustrated in FIG. 109D, a Rapid Thermal Anneal (RTA) is conductedto crystallize the N+ doped poly-crystalline silicon or amorphoussilicon layers 10906 of first Si/SiO2 layer 10923, second Si/SiO2 layer10925, and third Si/SiO2 layer 10927, forming crystallized N+ siliconlayers 10916. Temperatures during this RTA may be as high asapproximately 800° C. Alternatively, an optical anneal, such as, forexample, a laser anneal, could be performed alone or in combination withthe RTA or other annealing processes.

As illustrated in FIG. 109E, oxide 10929, third Si/SiO2 layer 10927,second Si/SiO2 layer 10925 and first Si/SiO2 layer 10923 may belithographically defined and plasma/RIE etched to form a portion of thememory cell structure, which now includes multiple layers of regions ofcrystallized N+ silicon 10926 (previously crystallized N+ silicon layers10916) and oxide 10922. Thus, these transistor elements or portions havebeen defined by a common lithography step, which also may be describedas a single lithography step, same lithography step, or one lithographystep.

As illustrated in FIG. 109F, a gate dielectric and gate electrodematerial may be deposited, planarized with a chemical mechanical polish(CMP), and then lithographically defined and plasma/RIE etched to formgate dielectric regions 10928 which may either be self-aligned to andcovered by gate electrodes 10930 (shown), or cover the entirecrystallized N+ silicon regions 10926 and oxide regions 10922multi-layer structure. The gate stack including gate electrode 10930 andgate dielectric 10928 may be formed with a gate dielectric, such asthermal oxide, and a gate electrode material, such as poly-crystallinesilicon. Alternatively, the gate dielectric may be an atomic layerdeposited (ALD) material that is paired with a work function specificgate metal according to an industry standard of high k metal gateprocess schemes described previously. Furthermore, the gate dielectricmay be formed with a rapid thermal oxidation (RTO), a low temperatureoxide deposition or low temperature microwave plasma oxidation of thesilicon surfaces and then a gate electrode such as tungsten or aluminummay be deposited.

As illustrated in FIG. 109G, the entire structure may be covered with agap fill oxide 10932, which may be planarized with chemical mechanicalpolishing. The oxide 10932 is shown transparently in the figure forclarity, along with word-line regions (WL) 10950, coupled with andcomposed of gate electrodes 10930, and source-line regions (SL) 10952,composed of crystallized N+ silicon regions 10926.

As illustrated in FIG. 109H, bit-line (BL) contacts 10934 may belithographically defined, etched with plasma/RIE through oxide 10932,the three crystallized N+ silicon regions 10926, and associated oxidevertical isolation regions to connect substantially all memory layersvertically, and photoresist removed. Resistance change memory material10938, such as, for example, hafnium oxides or titanium oxides, may thenbe deposited, preferably with atomic layer deposition (ALD). Theelectrode for the resistance change memory element may then be depositedby ALD to form the electrode/BL contact 10934. The excess depositedmaterial may be polished to planarity at or below the top of oxide10932. Each BL contact 10934 with resistive change material 10938 may beshared among substantially all layers of memory, shown as three layersof memory in FIG. 109H.

As illustrated in FIG. 109I, BL metal lines 10936 may be formed andconnected to the associated BL contacts 10934 with resistive changematerial 10938. Contacts and associated metal interconnect lines (notshown) may be formed for the WL and SL at the memory array edges. A thrulayer via 10960 (not shown) may be formed to electrically couple the BL,SL, and WL metallization to the acceptor substrate peripheral circuitryvia an acceptor wafer metal connect pad 10980 (not shown).

FIG. 109J1 is a cross sectional cut II view of FIG. 109J, while FIG.109J2 is a cross sectional cut III view of FIG. 109J. FIG. 109J1 showsBL metal line 10936, oxide 10932, BL contact/electrode 10934, resistivechange material 10938, WL regions 10950, gate dielectric 10928,crystallized N+ silicon regions 10926, and peripheral circuits substrate10902. The BL contact/electrode 10934 couples to one side of the threelevels of resistive change material 10938. The other side of theresistive change material 10938 is coupled to crystallized N+ regions10926. FIG. 109J2 shows BL metal lines 10936, oxide 10932, gateelectrode 10930, gate dielectric 10928, crystallized N+ silicon regions10926, interlayer oxide region (‘ox’), and peripheral circuits substrate10902. The gate electrode 10930 is common to substantially all sixcrystallized N+ silicon regions 10926 and forms six two-sided gatedjunction-less transistors as memory select transistors.

As illustrated in FIG. 109K, a single exemplary two-sided gatedjunction-less transistor on the first Si/SiO2 layer 10923 may includecrystallized N+ silicon region 10926 (functioning as the source, drain,and transistor channel), and two gate electrodes 10930 with associatedgate dielectrics 10928. The transistor is electrically isolated frombeneath by oxide layer 10908.

This flow may enable the formation of a resistance-based multi-layer or3D memory array with zero additional masking steps per memory layer,which utilizes poly-crystalline silicon junction-less transistors andhas a resistance-based memory element in series with a selecttransistor, and is constructed by layer transfers of wafer sized dopedpoly-crystalline silicon layers, and this 3D memory array may beconnected to an underlying multi-metal layer semiconductor device.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 109A through 109K are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the RTAs and/or opticalanneals of the N+ doped poly-crystalline or amorphous silicon layers10906 as described for FIG. 109D may be performed after each Si/SiO2layer is formed in FIG. 109C. Additionally, N+ doped poly-crystalline oramorphous silicon layer 10906 may be doped P+, or with a combination ofdopants and other polysilicon network modifiers to enhance the RTA oroptical annealing and subsequent crystallization and lower the N+silicon layer 10916 resistivity. Moreover, doping of each crystallizedN+ layer may be slightly different to compensate for interconnectresistances. Furthermore, each gate of the double gated 3D resistancebased memory can be independently controlled for better control of thememory cell. Many other modifications within the scope of the inventionwill suggest themselves to such skilled persons after reading thisspecification. Thus the invention is to be limited only by the appendedclaims.

As illustrated in FIGS. 110A to 110J, an alternative embodiment of aresistance-based 3D memory with zero additional masking steps per memorylayer may be constructed with methods that are suitable for 3D ICmanufacturing. This 3D memory utilizes poly-crystalline siliconjunction-less transistors that may have either a positive or a negativethreshold voltage, a resistance-based memory element in series with aselect or access transistor, and may have the periphery circuitry layerformed or layer transferred on top of the 3D memory array.

As illustrated in FIG. 110A, a silicon oxide layer 11004 may bedeposited or grown on top of silicon substrate 11002.

As illustrated in FIG. 110B, a layer of N+ doped poly-crystalline oramorphous silicon 11006 may be deposited. The amorphous silicon orpoly-crystalline silicon layer 11006 may be deposited using a chemicalvapor deposition process, such as LPCVD or PECVD, or other processmethods, and may be deposited doped with N+ dopants, such as, forexample, Arsenic or Phosphorous, or may be deposited un-doped andsubsequently doped with, such as, for example, ion implantation or PLAD(PLasma Assisted Doping) techniques. Silicon Oxide 11020 may then bedeposited or grown. This now forms the first Si/SiO2 layer 11023comprised of N+ doped poly-crystalline or amorphous silicon layer 11006and silicon oxide layer 11020.

As illustrated in FIG. 110C, additional Si/SiO2 layers, such as, forexample, second Si/SiO2 layer 11025 and third Si/SiO2 layer 11027, mayeach be formed as described in FIG. 110B. Oxide layer 11029 may bedeposited to electrically isolate the top N+ doped poly-crystalline oramorphous silicon layer.

As illustrated in FIG. 110D, a Rapid Thermal Anneal (RTA) is conductedto crystallize the N+ doped poly-crystalline silicon or amorphoussilicon layers 11006 of first Si/SiO2 layer 11023, second Si/SiO2 layer11025, and third Si/SiO2 layer 11027, forming crystallized N+ siliconlayers 11016. Alternatively, an optical anneal, such as, for example, alaser anneal, could be performed alone or in combination with the RTA orother annealing processes. Temperatures during this step could be ashigh as approximately 700° C., and could even be as high as, forexample, 1400° C. Since there are no circuits or metallizationunderlying these layers of crystallized N+ silicon, very hightemperatures (such as, for example, 1400° C.) can be used for the annealprocess, leading to very good quality poly-crystalline silicon with fewgrain boundaries and very high carrier mobilities approaching those ofmono-crystalline crystal silicon.

As illustrated in FIG. 110E, oxide 11029, third Si/SiO2 layer 11027,second Si/SiO2 layer 11025 and first Si/SiO2 layer 11023 may belithographically defined and plasma/RIE etched to form a portion of thememory cell structure, which now includes multiple layers of regions ofcrystallized N+ silicon 11026 (previously crystallized N+ silicon layers11016) and oxide 11022. Thus, these transistor elements or portions havebeen defined by a common lithography step, which also may be describedas a single lithography step, same lithography step, or one lithographystep.

As illustrated in FIG. 110F, a gate dielectric and gate electrodematerial may be deposited, planarized with a chemical mechanical polish(CMP), and then lithographically defined and plasma/RIE etched to formgate dielectric regions 11028 which may either be self-aligned to andcovered by gate electrodes 11030 (shown), or cover the entirecrystallized N+ silicon regions 11026 and oxide regions 11022multi-layer structure. The gate stack including gate electrode 11030 andgate dielectric 11028 may be formed with a gate dielectric, such asthermal oxide, and a gate electrode material, such as poly-crystallinesilicon. Alternatively, the gate dielectric may be an atomic layerdeposited (ALD) material that is paired with a work function specificgate metal according to an industry standard of high k metal gateprocess schemes described previously. Additionally, the gate dielectricmay be formed with a rapid thermal oxidation (RTO), a low temperatureoxide deposition or low temperature microwave plasma oxidation of thesilicon surfaces and then a gate electrode such as tungsten or aluminummay be deposited.

As illustrated in FIG. 110G, the entire structure may be covered with agap fill oxide 11032, which may be planarized with chemical mechanicalpolishing. The oxide 11032 is shown transparently in the figure forclarity, along with word-line regions (WL) 11050, coupled with andcomposed of gate electrodes 11030, and source-line regions (SL) 11052,composed of crystallized N+ silicon regions 11026.

As illustrated in FIG. 110H, bit-line (BL) contacts 11034 may belithographically defined, etched along with plasma/RIE through oxide11032, the three crystallized N+ silicon regions 11026, and theassociated oxide vertical isolation regions to connect substantially allmemory layers vertically. BL contacts 11034 may then be processed by aphotoresist removal. Resistance change memory material 11038, such ashafnium oxides or titanium oxides, may then be deposited, preferablywith atomic layer deposition (ALD). The electrode for the resistancechange memory element may then be deposited by ALD to form theelectrode/BL contact 11034. The excess deposited material may bepolished to planarity at or below the top of oxide 11032. Each BLcontact 11034 with resistive change material 11038 may be shared amongsubstantially all layers of memory, shown as three layers of memory inFIG. 110H.

As illustrated in FIG. 110I, BL metal lines 11036 may be formed andconnected to the associated BL contacts 11034 with resistive changematerial 11038. Contacts and associated metal interconnect lines (notshown) may be formed for the WL and SL at the memory array edges.

As illustrated in FIG. 110J, peripheral circuits 11078 may beconstructed and then layer transferred, using methods describedpreviously such as, for example, ion-cut with replacement gates, to thememory array, and then thru layer vias (not shown) may be formed toelectrically couple the periphery circuitry to the memory array BL, WL,SL and other connections such as, for example, power and ground.Alternatively, the periphery circuitry may be formed and directlyaligned to the memory array and silicon substrate 11002 utilizing thelayer transfer of wafer sized doped layers and subsequent processing,such as, for example, the junction-less, RCAT, V-groove, or bipolartransistor formation flows as previously described.

This flow may enable the formation of a resistance-based multi-layer or3D memory array with zero additional masking steps per memory layer,which utilizes poly-crystalline silicon junction-less transistors andhas a resistance-based memory element in series with a selecttransistor, and is constructed by layer transfers of wafer sized dopedpoly-crystalline silicon layers, and this 3D memory array may beconnected to an overlying multi-metal layer semiconductor device orperiphery circuitry.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 110A through 110J are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the RTAs and/or opticalanneals of the N+ doped poly-crystalline or amorphous silicon layers11006 as described for FIG. 110D may be performed after each Si/SiO2layer is formed in FIG. 110C. Additionally, N+ doped poly-crystalline oramorphous silicon layer 11006 may be doped P+, or with a combination ofdopants and other polysilicon network modifiers to enhance the RTA oroptical annealing crystallization and subsequent crystallization, andlower the N+ silicon layer 11016 resistivity. Moreover, doping of eachcrystallized N+ layer may be slightly different to compensate forinterconnect resistances. Besides, each gate of the double gated 3Dresistance based memory can be independently controlled for bettercontrol of the memory cell. Furthermore, by proper choice of materialsfor memory layer transistors and memory layer wires (e.g., by usingtungsten and other materials that withstand high temperature processingfor wiring), standard CMOS transistors may be processed at hightemperatures (e.g., >700° C.) to form the periphery circuitry 11078.Many other modifications within the scope of the invention will suggestthemselves to such skilled persons after reading this specification.Thus the invention is to be limited only by the appended claims.

An alternative embodiment of this present invention may be a monolithic3D DRAM we call NuDRAM. It may utilize layer transfer and cleavingmethods described in this document. It may provide high-quality singlecrystal silicon at low effective thermal budget, leading to considerableadvantage over prior art.

One embodiment of this present invention may be constructed with theprocess flow depicted in FIG. 88(A)-(F). FIG. 88(A) describes the firststep in the process. A p-wafer 8801 may be implanted with n type dopantto form an n+ layer 8802, following which an RTA may be performed.Alternatively, the n+ layer 8802 may be formed by epitaxy.

FIG. 88(B) shows the next step in the process. Hydrogen may be implantedinto the wafer at a certain depth in the p− region 8801. Final positionof the hydrogen is depicted by the dotted line 8803.

FIG. 88(C) describes the next step in the process. The wafer may beattached to a temporary carrier wafer 8804 using an adhesive. Forexample, one could use a polyimide adhesive from Dupont for this purposealong with a temporary carrier wafer 8804 made of glass. The wafer maythen be cleaved at the hydrogen plane 8803 using any cleave methoddescribed in this document. After cleave, the cleaved surface ispolished with CMP and an oxide 8805 is deposited on this surface. Thestructure of the wafer after substantially all these processes arecarried out is shown in FIG. 88(C).

FIG. 88(D) illustrates the next step in the process. A wafer with DRAMperipheral circuits 8806 such as sense amplifiers, row decoders, etc.may now be used as a base on top of which the wafer in FIG. 88(C) isbonded, using oxide-to-oxide bonding at surface 8807. The temporarycarrier 8804 may then be removed. Then, a step of masking, etching, andoxidation may be performed, to define rows of diffusion, isolated byoxide similarly to 8905 of FIG. 89 (B). The rows of diffusion andisolation may be aligned with the underlying peripheral circuits 8806.After forming isolation regions, RCATs may be constructed by etching,and then depositing gate dielectric 8809 and gate electrode 8808. Thisprocedure is further explained in the descriptions for FIG. 67. The gateelectrode mask may be aligned to the underlying peripheral circuits8806. An oxide layer 8810 may be deposited and polished with CMP.

FIG. 88(E) shows the next step of the process. A second RCAT layer 8812may be formed atop the first RCAT layer 8811 using steps similar to FIG.88(A)-(D). These steps could be repeated multiple times to form themultilayer 3D DRAM.

The next step of the process is described with respect to FIG. 88(F).Via holes may be etched to source 8814 and drain 8815 throughsubstantially all of the layers of the stack. As this step is alsoperformed in alignment with the peripheral circuits 8806, an etch stopcould be designed or no vulnerable element should be placed underneaththe designated etch locations. This is similar to a conventional DRAMarray wherein the gates 8816 of multiple RCAT transistors are connectedby poly line or metal line perpendicular to the plane of theillustration in FIG. 88. This connection of gate electrodes may form theword-line, similar to that illustrated in FIGS. 89A-D. The layout mayspread the word-lines of the multilayer DRAM structure so that for eachlayer there may be one vertical contact hole connection to allowperipheral circuits 8806 to control each layer's word-lineindependently. Via holes may then be filled with heavily dopedpolysilicon 8813. The heavily doped polysilicon 8813 may be constructedusing a low temperature (below 400° C.) process such as PECVD. Theheavily doped polysilicon 8813 may not only improve the contact ofmultiple sources, drains, and word-lines of the 3D DRAM, but also servethe purpose of separating adjacent p− layers 8817 and 8818.Alternatively, oxide may be utilized for isolation. Multiple layers ofinterconnects and vias may then be constructed to form Bit-Lines 8815and Source-Lines 8814 to complete the DRAM array. While RCAT transistorsare shown in FIG. 88, a process flow similar to FIG. 88A-F can bedeveloped for other types of low-temperature processed stackabletransistors as well. For example, V-groove transistors and othertransistors described in other embodiments of the present invention canbe developed.

FIG. 89(A)-(D) show the side-views, layout, and schematic of one part ofthe NuDRAM array described in FIG. 88(A)-(F). FIG. 89(A) shows oneparticular cross-sectional view of the NuDRAM array. The Bit-Lines (BL)8902 may run in a direction perpendicular to the word-lines (WL) 8904and source-lines (SL) 8903.

A cross-sectional view taken along the plane indicated by the brokenline as shown in FIG. 89(B). Oxide isolation regions 8905 may separatep− layers 8906 of adjacent transistors. WL 8907 may include, forexample, gate electrodes of each transistor connected together.

A layout of this array is shown in FIG. 89(C). The WL wiring 8908 and SLwiring 8909 may be perpendicular to the BL wiring 8910. A schematic ofthe NuDRAM array (FIG. 89(D)) reveals connections for WLs, BLs and SLsat the array level.

Another variation embodiment of the present invention is described inFIG. 90(A)-(F). FIG. 90(A) describes the first step in the process. A p−wafer 9001 may include an n+ epi layer 9002 and a p− epi layer 9003grown over the n+ epi layer. Alternatively, these layers could be formedwith implant. An oxide layer 9004 may be grown or deposited over thewafer as well.

FIG. 90(B) shows the next step in the process. Hydrogen H+, or otheratomic species, may be implanted into the wafer at a certain depth inthe n+ region 9002. The final position of the hydrogen is depicted bythe dotted line 9005.

FIG. 90(C) describes the next step in the process. The wafer may beflipped and attached to a wafer with DRAM peripheral circuits 9006 usingoxide-to-oxide bonding. The wafer may then be cleaved at the hydrogenplane 9005 using low temperature (less than 400° C.) cleave methodsdescribed in this document. After cleave, the cleaved surface may bepolished with CMP.

As shown in FIG. 90(D), a step of masking, etching, and low temperatureoxide deposition may be performed, to define rows of diffusion, isolatedby said oxide. Said rows of diffusion and isolation may be aligned withthe underlying peripheral circuits 9006. After forming isolationregions, RCATs may be constructed with masking, etch, gate dielectric9009 and gate electrode 9008 deposition. The procedure for this isexplained in the description for FIG. 67. Said gates may be aligned tothe underlying peripheral circuits 9006. An oxide layer 9010 may bedeposited and polished with CMP.

FIG. 90(E) shows the next step of the process. A second RCAT layer 9012may be formed atop the first RCAT layer 9011 using steps similar to FIG.90(A)-(D). These steps could be repeated multiple times to form themultilayer 3D DRAM.

The next step of the process is described in FIG. 90(F). Via holes maybe etched to the source and drain connections through substantially allof the layers in the stack, similar to a conventional DRAM array whereinthe gate electrodes 9016 of multiple RCAT transistors are connected bypoly line perpendicular to the plane of the illustration in FIG. 90.This connection of gate electrodes may form the word-line. The layoutmay spread the word-lines of the multilayer DRAM structure so that foreach layer there may be one vertical hole to allow the peripheralcircuit 9006 to control each layer word-line independently. Via holesmay then be filled with heavily doped polysilicon 9013. The heavilydoped silicon 9013 may be constructed using a low temperature processbelow 400° C. such as PECVD. Multiple layers of interconnects and viasmay then be constructed to form bit-lines 9015 and source-lines 9014 tocomplete the DRAM array. Array organization of the NuDRAM described inFIG. 90 is similar to FIG. 89. While RCAT transistors are shown in FIG.90, a process flow similar to FIG. 90 can be developed for other typesof low-temperature processed stackable transistors as well. For example,V-groove transistors and other transistors previously described in otherembodiments of this present invention can be developed.

Yet another flow for constructing NuDRAMs is shown in FIG. 91A-L. Theprocess description begins in FIG. 91A with forming shallow trenchisolation 9102 in an SOI p− wafer 9101. The buried oxide layer isindicated as 9119.

Following this, a gate trench etch 9103 may be performed as illustratedin FIG. 91B. FIG. 91B shows a cross-sectional view of the NuDRAM in theYZ plane, compared to the XZ plane for FIG. 91A (therefore the shallowtrench isolation 9102 is not shown in FIG. 91B).

The next step in the process is illustrated in FIG. 91C. A gatedielectric layer 9105 may be formed and the RCAT gate electrode 9104 maybe formed using procedures similar to FIG. 67E. Ion implantation maythen be carried out to form source and drain n+ regions 9106.

FIG. 91D shows an inter-layer dielectric 9107 formed and polished.

FIG. 91E reveals the next step in the process. Another p− wafer 9108 maybe taken, an oxide 9109 may be grown on p− wafer 9108 following whichhydrogen H+, or other atomic species, may be implanted at a certaindepth 9110 for cleave purposes.

This “higher layer” 9108 may then be flipped and bonded to the lowerwafer 9101 using oxide-to-oxide bonding. A cleave may then be performedat the hydrogen plane 9110, following which a CMP may be performedresulting in the structure as illustrated in FIG. 91F.

FIG. 91G shows the next step in the process. Another layer of RCATs 9113may be constructed using procedures similar to those shown in FIG.91B-D. This layer of RCATs may be aligned to features in the bottomwafer 9101.

As shown in FIG. 91H, one or more layers of RCATs 9114 can then beconstructed using procedures similar to those shown in FIG. 91E-G.

FIG. 91I illustrates vias 9115 being formed to different n+ regions andalso to WL layers. These vias 9115 may be constructed with heavily dopedpolysilicon.

FIG. 91J shows the next step in the process where a Rapid Thermal Anneal(RTA) may be done to activate implanted dopants and to crystallize polySi regions of substantially all layers.

FIG. 91K illustrates bit-lines BLs 9116 and source-lines SLs 9117 beingformed.

Following the formations of BLs 9116 and SL 9117, FIG. 91L shows a newlayer of transistors and vias for DRAM peripheral circuits 9118 formedusing procedures described previously (e.g., V-groove MOSFETs can beformed as described in FIG. 29A-G). These peripheral circuits 9118 maybe aligned to the DRAM transistor layers below. DRAM transistors forthis embodiment can be of any type (either high temperature (i.e., >400°C.) processed or low temperature (i.e., <400° C.) processedtransistors), while peripheral circuits may be low temperature processedtransistors since they are constructed after Aluminum or Copper wiringlayers 9116 and 9117. Array architecture for the embodiment shown inFIG. 91 may be similar to the one indicated in FIG. 89.

A variation of the flow shown in FIG. 91A-L may be used as analternative process for fabricating NuDRAMs. Peripheral circuit layersmay first be constructed with substantially all steps complete fortransistors except the RTA. One or more levels of tungsten metal may beused for local wiring of these peripheral circuits. Following this,multiple layers of RCATs may be constructed with layer transfer asdescribed in FIG. 91, after which an RTA may be conducted. Highlyconductive copper or aluminum wire layers may then be added for thecompletion of the DRAM flow. This flow reduces the fabrication cost bysharing the RTA, the high temperature steps, doing them once forsubstantially all crystallized layers and also allows the use of similardesign for the 3D NuDRAM peripheral circuit as used in conventional 2DDRAM. For this process flow, DRAM transistors may be of any type, andare not restricted to low temperature etch-defined transistors such asRCAT or V-groove transistors.

An illustration of a NuDRAM constructed with partially depleted SOItransistors is given in FIG. 92A-F. FIG. 92A describes the first step inthe process. A p− wafer 9201 may have an oxide layer 9202 grown over it.FIG. 92B shows the next step in the process. Hydrogen H+ may beimplanted into the wafer at a certain depth in the p− region 9201. Thefinal position of the hydrogen is depicted by the dotted line 9203. FIG.92C describes the next step in the process. A wafer with DRAM peripheralcircuits 9204 may be prepared. This wafer may have transistors that havenot seen RTA processes. Alternatively, a weak or partial RTA for theperipheral circuits may be used. Multiple levels of tungsteninterconnect to connect together transistors in 9204 are prepared. Thewafer from FIG. 92B may be flipped and attached to the wafer with DRAMperipheral circuits 9204 using oxide-to-oxide bonding. The wafer maythen be cleaved at the hydrogen plane 9203 using any cleave methoddescribed in this document. After cleave, the cleaved surface may bepolished with CMP. FIG. 92D shows the next step in the process. A stepof masking, etching, and low temperature oxide deposition may beperformed, to define rows of diffusion, isolated by said oxide. Saidrows of diffusion and isolation may be aligned with the underlyingperipheral circuits 9204. After forming isolation regions, partiallydepleted SOI (PD-SOI) transistors may be constructed with formation of agate dielectric 9207, a gate electrode 9205, and then patterning andetch of 9207 and 9205 followed by formation of ion implantedsource/drain regions 9208. Note that no RTA may be done at this step toactivate the implanted source/drain regions 9208. The masking step inFIG. 92D may be aligned to the underlying peripheral circuits 9204. Anoxide layer 9206 may be deposited and polished with CMP. FIG. 92E showsthe next step of the process. A second PD-SOI transistor layer 9209 maybe formed atop the first PD-SOI transistor layer using steps similar toFIG. 92A-D. These may be repeated multiple times to form the multilayer3D DRAM. An RTA to activate dopants and crystallize polysilicon regionsin substantially all the transistor layers may then be conducted. Thenext step of the process is described in FIG. 92F. Via holes 9210 may bemasked and may be etched to word-lines and source and drain connectionsthrough substantially all of the layers in the stack. Note that thegates of transistors 9213 are connected together to form word-lines in asimilar fashion to FIG. 89. Via holes may then be filled with a metalsuch as tungsten. Alternatively, heavily doped polysilicon may be used.Multiple layers of interconnects and vias may be constructed to formBit-Lines 9211 and Source-Lines 9212 to complete the DRAM array. Arrayorganization of the NuDRAM described in FIG. 92 is similar to FIG. 89.

For the purpose of programming transistors, a single type of toptransistor could be sufficient. Yet for logic type circuitry twocomplementing transistors might be helpful to allow CMOS type logic.Accordingly the above described various mono-type transistor flows couldbe performed twice. First perform substantially all the steps to buildthe ‘n’ type, and than do an additional layer transfer to build the ‘p’type on top of it.

An additional alternative is to build both ‘n’ type and ‘p’ typetransistors on the same layer. The challenge is to form thesetransistors aligned to the underlying layers 808. The innovativesolution is described with the help of FIGS. 30 to 33. The flow could beapplied to any transistor constructed in a manner suitable for wafertransfer including, but not limited to horizontal or vertical MOSFETs,JFETs, horizontal and vertical junction-less transistors, RCATs,Spherical-RCATs, etc. The main difference is that now the donor wafer3000 is pre-processed to build not just one transistor type but bothtypes by comprising alternating rows throughout donor wafer 3000 for thebuild of rows of ‘n’ type transistors 3004 and rows of ‘p’ typetransistors 3006 as illustrated in FIG. 30. FIG. 30 also includes a fourcardinal directions indicator 3040, which will be used through FIG. 33to assist the explanation. The width of the n-type rows 3004 is Wn andthe width of the p-type rows 3006 is Wp and their sum W 3008 is thewidth of the repeating pattern. The rows traverse from East to West andthe alternating repeats substantially all the way from North to South.The donor wafer rows 3004 and 3006 may extend in length East to West bythe acceptor die width plus the maximum donor wafer to acceptor wafermisalignment, or alternatively, may extend the entire length of a donorwafer East to West. In fact the wafer could be considered as dividedinto reticle projections which in most cases may contain a few dies perimage or step field. In most cases, the scribe line designed for futuredicing of the wafer to individual dies may be more than 20 microns wide.The wafer to wafer misalignment may be about 1 micron. Accordingly,extending patterns into the scribe line may allow full use of thepatterns within the die boundaries with minimal effect on the dicingscribe lines. Wn and Wp could be set for the minimum width of thecorresponding transistor, n-type transistor and p-type transistorrespectively, plus its isolation in the selected process node. The wafer3000 also has an alignment mark 3020 which is on the same layers of thedonor wafer as the n 3004 and p 3006 rows and accordingly could be usedlater to properly align additional patterning and processing steps tosaid n 3004 and p 3006 rows.

The donor wafer 3000 will be placed on top of the main wafer 3100 for alayer transfer as described previously. The state of the art allows forvery good angular alignment of this bonding step but it is difficult toachieve a better than approximately 1 micron position alignment.

Persons of ordinary skill in the art will appreciate that the directionsNorth, South, East and West are used for illustrative purposes only,have no relationship to true geographic directions, that the North-Southdirection could become the East-West direction (and vice versa) bymerely rotating the wafer 90 degrees and that the rows of ‘n’ typetransistors 3004 and rows of ‘p’ type transistors 3006 could also runNorth-South as a matter of design choice with corresponding adjustmentsto the rest of the fabrication process. Such skilled persons willfurther appreciate that the rows of ‘n’ type transistors 3004 and rowsof ‘p’ type transistors 3006 can have many different organizations as amatter of design choice. For example, the rows of ‘n’ type transistors3004 and rows of ‘p’ type transistors 3006 can each comprise a singlerow of transistors in parallel, multiple rows of transistors inparallel, multiple groups of transistors of different dimensions andorientations and types (either individually or in groups), and differentratios of transistor sizes or numbers between the rows of ‘n’ typetransistors 3004 and rows of ‘p’ type transistors 3006, etc. Thus thescope of the invention is to be limited only by the appended claims.

FIG. 31 illustrates the main wafer 3100 with its alignment mark 3120 andthe transferred layer 3000L of the donor wafer 3000 with its alignmentmark 3020. The misalignment in the East-West direction is DX 3124 andthe misalignment in the North-South direction is DY 3122. For simplicityof the following explanations, the alignment marks 3120 and 3020 may beassumed set so that the alignment mark of the transferred layer 3020 isalways north of the alignment mark of the base wafer 3120, though thecases where alignment mark 3020 is either perfectly aligned with (withintolerances) or south of alignment mark 3120 are handled in anappropriately similar manner. In addition, these alignment marks may beplaced in only a few locations on each wafer, within each step field,within each die, within each repeating pattern W, or in other locationsas a matter of design choice.

In the construction of this described monolithic 3D Integrated Circuitsthe objective is to connect structures built on layer 3000L to theunderlying main wafer 3100 and to structures on 808 layers at about thesame density and accuracy as the connections between layers in 808,which may need alignment accuracies on the order of tens of nm orbetter.

In the direction East-West the approach will be the same as wasdescribed before with respect to FIGS. 21 through 29. The pre-fabricatedstructures on the donor wafer 3000 are the same regardless of themisalignment DX 3124. Therefore just like before, the pre-fabricatedstructures may be aligned using the underlying alignment mark 3120 toform the transistors out of the rows of ‘n’ type transistors 3004 androws of ‘p’ type transistors 3006 by etching and additional processes asdescribed regardless of DX. In the North-South direction it is nowdifferent as the pattern does change. Yet the advantage of the proposedstructure of the repeating pattern in the North-South direction ofalternating rows illustrated in FIG. 30 arises from the fact that forevery distance W 3008, the pattern repeats. Accordingly the effectivealignment uncertainty may be reduced to W 3008 as the pattern in theNorth-South direction keeps repeating every W.

So the effective alignment uncertainty may be calculated as to how manyWs-full patterns of ‘n’ 3004 and ‘p’ 3006 row pairs would fit in DY 3122and what would be the residue Rdy 3202 (remainder of DY modulo W,0<=Rdy<W) as illustrated in FIG. 32. Accordingly, to properly align tothe nearest n 3004 and p 3006 in the North-South direction, thealignment will be to the underlying alignment mark 3120 offset by Rdy3202. Accordingly, the alignment may be done based on the misalignmentbetween the alignment marks of the acceptor wafer alignment mark 3120and the donor wafer alignment marks 3020 by taking into account therepeating distance W 3008 and calculating the resultant required ofoffset Rdy 3202. Alignment mark 3120, covered by the wafer 3000L duringalignment, may be visible and usable to the stepper or lithographic toolalignment system when infra-red (IR) light and optics are being used.

Alternatively, multiple alignment marks on the donor wafer could be usedas illustrated in FIG. 69. The donor wafer alignment mark 3020 may bereplicated precisely every W 6920 in the North to South direction for adistance to cover the full extent of potential North to Southmisalignment M 6922 between the donor wafer and the acceptor wafer. Theresidue Rdy 3202 may therefore be the North to South misalignmentbetween the closest donor wafer alignment mark 6920C and the acceptorwafer alignment mark 3120. Accordingly, instead of alignment to theunderlying alignment mark 3120 offset by Rdy 3202, alignment can be tothe donor layer's closest alignment mark 6920C. Accordingly, thealignment may be done based on the misalignment between the alignmentmarks of the acceptor wafer alignment mark 3120 and the donor waferalignment marks 6920 by choosing the closest alignment mark 6920C on thedonor wafer.

The illustration in FIG. 69 was made to simplify the explanation, and inactual usage the alignment marks might take a larger area than W×W. Insuch a case, to avoid having the alignment marks 6920 overlapping eachother, an offset could be used with proper marking to allow properalignment.

Each wafer that will be processed accordingly through this flow willhave a specific Rdy 3202 which will be subject to the actualmisalignment DY 3122. But the masks used for patterning the variouspatterns need to be pre-designed and fabricated and remain the same forsubstantially all wafers (processed for the same end-device) regardlessof the actual misalignment. In order to improve the connection betweenstructures on the transferred layer 3000L and the underlying main wafer3100, the underlying wafer 3100 is designed to have a landing zone of astrip 33A04 going North-South of length W 3008 plus any extensionnecessary for the via design rules, as illustrated in FIG. 33A. Thelanding zone extension, in length or width, for via design rules mayinclude compensation for angular misalignment due to the wafer to waferbonding that is not compensated for by the stepper overlay algorithms,and may include uncompensated donor wafer bow and warp. The strip 33A04may be part of the base wafer 3100 and accordingly aligned to itsalignment mark 3120. Via 33A02 going down and being part of a top layer3000L pattern (aligned to the underlying alignment mark 3120 with Rdyoffset) will be connected to the landing zone 33A04. Via 33A02 may bedrawn in the database (not shown) so that it is positioned approximatelyat the center of the strip 33A04, and, hence, may be away from the endsof the strip 33A04 at distances greater than approximately the nominallayer to layer misalignment margin.

Alternatively a North-South landing strip 33B04 with at least W length,plus extensions per the via design rules and other compensationsdescribed above, may be made on the upper layer 3000L and accordinglyaligned to the underlying alignment mark 3120 with Rdy offset, thusconnected to the via 33B02 coming ‘up’ and being part of the underlyingpattern aligned to the underlying alignment mark 3120 (with no offset).

An example of a process flow to create complementary transistors on asingle transferred layer for CMOS logic is as follows. First, a donorwafer may be preprocessed to be prepared for the layer transfer. Thiscomplementary donor wafer may be specifically processed to createrepeating rows 3400 of p and n wells whereby their combined widths is W3008 as illustrated in FIG. 34A. Repeating rows 3400 may be as long asan acceptor die width plus the maximum donor wafer to acceptor wafermisalignment, or alternatively, may extend the entire length of a donorwafer. FIG. 34A may be rotated 90 degrees with respect to FIG. 30 asindicated by the four cardinal directions indicator, to be in the sameorientation as subsequent FIGS. 34B through 35G.

FIG. 34B is a cross-sectional drawing illustration of a pre-processedwafer used for a layer transfer. A P− wafer 3402 is processed to have a“buried” layer of N+ 3404 and of P+ 3406 by masking, ion implantation,and activation in repeated widths of W 3008.

This is followed by a P− epi growth (epitaxial growth) 3408 and a mask,ion implantation, and anneal of N− regions 3410 in FIG. 34C.

Next, a shallow P+ 3412 and N+ 3414 are formed by mask, shallow ionimplantation, and RTA activation as shown in FIG. 34D.

FIG. 34E is a drawing illustration of the pre-processed wafer for alayer transfer by an implant of an atomic species, such as H+, preparingthe SmartCut “cleaving plane” 3416 in the lower part of the deep N+ & P+regions. A thin layer of oxide 3418 may be deposited or grown tofacilitate the oxide-oxide bonding to the layer 808. This oxide 3418 maybe deposited or grown before the H+ implant, and may comprise differingthicknesses over the P+ 3412 and N+ 3414 regions so as to allow an evenH+ implant range stopping to facilitate a level and continuous Smart Cutcleave plane 3416. Adjusting the depth of the H+ implant if needed couldbe achieved in other ways including different implant depth setting forthe P+ 3412 and N+ 3414 regions.

Now a layer-transfer-flow is performed, as illustrated in FIG. 20, totransfer the pre-processed striped multi-well single crystal siliconwafer on top of 808 as shown in FIG. 35A. The cleaved surface 3502 mayor may not be smoothed by a combination of CMP and chemical polishtechniques.

A variation of the p & n well stripe donor wafer preprocessing above isto also preprocess the well isolations with shallow trench etching,dielectric fill, and CMP prior to the layer transfer.

The step by step low temperature formation side views of the planar CMOStransistors on the complementary donor wafer (FIG. 34) is illustrated inFIGS. 35A to 35G. FIG. 35A illustrates the layer transferred on top ofwafer or layer 808 after the smart cut 3502 wherein the N+ 3404 & P+3406 are on top running in the East to West direction (i.e.,perpendicular to the plane of the drawing) and repeating widths in theNorth to South direction as indicated by cardinal 3500.

Then the substrate P+ 35B06 and N+ 35B08 source and 808 metal layer35B04 access openings, as well as the transistor isolation 35B02 aremasked and etched in FIG. 35B. This and substantially all subsequentmasking layers are aligned as described and shown above in FIG. 30-32and is illustrated in FIG. 35B where the layer alignment mark 3020 isaligned with offset Rdy to the base wafer layer 808 alignment mark 3120.

Utilizing an additional masking layer, the isolation region 35C02 isdefined by etching substantially all the way to the top of preprocessedwafer or layer 808 to provide full isolation between transistors orgroups of transistors in FIG. 35C. Then a Low-Temperature Oxide 35C04 isdeposited and chemically mechanically polished. Then a thin polish stoplayer 35C06 such as low temperature silicon nitride is depositedresulting in the structure illustrated in FIG. 35C.

The n-channel source 35D02, drain 35D04 and self-aligned gate 35D06 aredefined by masking and etching the thin polish stop layer 35C06 and thena sloped N+ etch as illustrated in FIG. 35D. The above is repeated onthe P+ to form the p-channel source 35D08, drain 35D10 and self-alignedgate 35D12 to create the complementary devices and form ComplementaryMetal Oxide Semiconductor (CMOS). Both sloped (35-90 degrees, 45 isshown) etches may be accomplished with wet chemistry or plasma etchingtechniques. This etch forms N+ angular source and drain extensions 35D12and P+ angular source and drain extension 35D14.

FIG. 35E illustrates the structure following deposition anddensification of a low temperature based Gate Dielectric 35E02, oralternatively a low temperature microwave plasma oxidation of thesilicon surfaces, to serve as the n & p MOSFET gate oxide, and thendeposition of a gate material 35E04, such as aluminum or tungsten.Alternatively, a high-k metal gate structure may be formed as follows.Following an industry standard HF/SC1/SC2 clean to create an atomicallysmooth surface, a high-k dielectric 35E02 is deposited. Thesemiconductor industry has chosen Hafnium-based dielectrics as theleading material of choice to replace SiO2 and Silicon oxynitride. TheHafnium-based family of dielectrics includes hafnium oxide and hafniumsilicate/hafnium silicon oxynitride. Hafnium oxide, HfO2, has adielectric constant twice as much as that of hafnium silicate/hafniumsilicon oxynitride (HfSiO/HfSiON k˜15). The choice of the metal iscritical for the device to perform properly. A metal replacing N+ polyas the gate electrode needs to have a work function of approximately 4.2eV for the device to operate properly and at the right thresholdvoltage. Alternatively, a metal replacing P+ poly as the gate electrodeneeds to have a work function of approximately 5.2 eV to operateproperly. The TiAl and TiAlN based family of metals, for example, couldbe used to tune the work function of the metal from 4.2 eV to 5.2 eV.The gate oxides and gate metals may be different between the n and pchannel devices, and is accomplished with selective removal of one typeand replacement of the other type.

FIG. 35F illustrates the structure following a chemical mechanicalpolishing of the metal gate 35E04 utilizing the nitride polish stoplayer 35C06. Finally a thick oxide 35G02 is deposited and contactopenings are masked and etched preparing the transistors to be connectedas illustrated in FIG. 35G. This figure also illustrates the layertransfer silicon via 35G04 masked and etched to provide interconnectionof the top transistor wiring to the lower layer 808 interconnect wiring35B04. This flow enables the formation of mono-crystalline top CMOStransistors that could be connected to the underlying multi-metal layersemiconductor device without exposing the underlying devices andinterconnects metals to high temperature. These transistors could beused as programming transistors of the antifuse on layer 807 or forother functions such as logic or memory in a 3D integrated circuit thatmay be electrically coupled to metal layers in preprocessed wafer orlayer 808. An additional advantage of this flow is that the SmartCut H+,or other atomic species, implant step is done prior to the formation ofthe MOS transistor gates avoiding potential damage to the gate function.

Persons of ordinary skill in the art will appreciate that while thetransistors fabricated in FIGS. 34A through 35G are shown with theirconductive channels oriented in a north-south direction and their gateelectrodes oriented in an east-west direction for clarity in explainingthe simultaneous fabrication of P-channel and N-channel transistors,that other orientations and organizations are possible. Such skilledpersons will further appreciate that the transistors may be rotated 90°with their gate electrodes oriented in a north-south direction. Forexample, it will be evident to such skilled persons that transistorsaligned with each other along an east-west row can either beelectrically isolated from each other with Low-Temperature Oxide 35C04or share source and drain regions and contacts as a matter of designchoice. Such skilled persons will also realize that rows of ‘n’ typetransistors 3004 may contain multiple N-channel transistors aligned in anorth-south direction and rows of ‘p’ type transistors 3006 may containmultiple P-channel transistors aligned in a north-south direction,specifically to form back-to-back sub-rows of P-channel and N-channeltransistors for efficient logic layouts in which adjacent sub-rows ofthe same type share power supply lines and connections. Many otherdesign choices are possible within the scope of the invention and willsuggest themselves to such skilled persons, thus the invention is to belimited only by the appended claims.

Alternatively, full CMOS devices may be constructed with a single layertransfer of wafer sized doped layers. The process flow will be describedbelow for the case of n-RCATs and p-RCATs, but may apply to any of theabove devices constructed out of wafer sized transferred doped layers.

As illustrated in FIGS. 95A to 95I, an n-RCAT and p-RCAT may beconstructed in a single layer transfer of wafer sized doped layer with aprocess flow that is suitable for 3D IC manufacturing.

As illustrated in FIG. 95A, a P− substrate donor wafer 9500 may beprocessed to include four wafer sized layers of N+ doping 9503, P−doping 9504, P+ doping 9506, and N− doping 9508. The P− layer 9504 mayhave the same or a different dopant concentration than the P− substrate9500. The four doped layers 9503, 9504, 9506, and 9508 may be formed byion implantation and thermal anneal. The layer stack may alternativelybe formed by successive epitaxially deposited doped silicon layers or bya combination of epitaxy and implantation and anneals. P− layer 9504 andN− layer 9508 may also have graded doping to mitigate transistorperformance issues, such as short channel effects. A screen oxide 9501may be grown or deposited before an implant to protect the silicon fromimplant contamination and to provide an oxide surface for later wafer towafer bonding. These processes may be done at temperatures above 400° C.as the layer transfer to the processed substrate with metalinterconnects has yet to be done.

As illustrated in FIG. 95B, the top surface of donor wafer 9500 may beprepared for oxide wafer bonding with a deposition of an oxide 9502 orby thermal oxidation of the N− layer 9508 to form oxide layer 9502, or are-oxidation of implant screen oxide 9501. A layer transfer demarcationplane 9599 (shown as a dashed line) may be formed in donor wafer 9500 orN+ layer 9503 (shown) by hydrogen implantation 9507 or other methods aspreviously described. Both the donor wafer 9500 and acceptor wafer 9510may be prepared for wafer bonding as previously described and then lowtemperature (less than approximately 400° C.) bonded. The portion of theN+ layer 9503 and the P− donor wafer substrate 9500 that are above thelayer transfer demarcation plane 9599 may be removed by cleaving andpolishing, or other low temperature processes as previously described.This process of an ion implanted atomic species, such as, for example,Hydrogen, forming a layer transfer demarcation plane, and subsequentcleaving or thinning, may be called ‘ion-cut’. Acceptor wafer 9510 mayhave similar meanings as wafer 808 previously described with referenceto FIG. 8.

As illustrated in FIG. 95C, the remaining N+ layer 9503′, P− doped layer9504, P+ doped layer 9506, N− doped layer 9508, and oxide layer 9502have been layer transferred to acceptor wafer 9510. The top surface ofN+ layer 9503′ may be chemically or mechanically polished smooth andflat. Now multiple transistors may be formed with low temperature (lessthan approximately 400° C.) processing and aligned to the acceptor wafer9510 alignment marks (not shown). For illustration clarity, the oxidelayers, such as 9502, used to facilitate the wafer to wafer bond are notshown in subsequent drawings.

As illustrated in FIG. 95D the transistor isolation region may belithographically defined and then formed by plasma/RIE etch removal ofportions of N+ doped layer 9503′, P− doped layer 9504, P+ doped layer9506, and N− doped layer 9508 to at least the top oxide of acceptorsubstrate 9510. Then a low-temperature gap fill oxide may be depositedand chemically mechanically polished, remaining in transistor isolationregion 9520. Thus formed are future RCAT transistor regions N+ doped9513, P− doped 9514, P+ doped 9516, and N− doped 9518.

As illustrated in FIG. 95E the N+ doped region 9513 and P− doped region9514 of the p-RCAT portion of the wafer are lithographically defined andremoved by either plasma/RIE etch or a selective wet etch. Then thep-RCAT recessed channel 9542 may be mask defined and etched. Therecessed channel surfaces and edges may be smoothed by wet chemical orplasma/RIE etching techniques to mitigate high field effects. Theseprocess steps form P+ source and drain regions 9526 and N− transistorchannel region 9528.

As illustrated in FIG. 95F, a gate oxide 9511 may be formed and a gatemetal material 9554 may be deposited. The gate oxide 9511 may be anatomic layer deposited (ALD) gate dielectric that is paired with a workfunction specific gate metal 9554 according to an industry standard ofhigh k metal gate process schemes described previously and targeted foran p-channel RCAT utility. Alternatively, the gate oxide 9511 may beformed with a low temperature oxide deposition or low temperaturemicrowave plasma oxidation of the silicon surfaces and then a gatematerial such as platinum or aluminum may be deposited. Then the gatematerial 9554 may be chemically mechanically polished, and the p-RCATgate electrode 9554′ defined by masking and etching.

As illustrated in FIG. 95G, a low temperature oxide 9550 may bedeposited and planarized, covering the formed p-RCAT so that theprocessing to form the n-RCAT may proceed.

As illustrated in FIG. 95H the n-RCAT recessed channel 9544 may be maskdefined and etched. The recessed channel surfaces and edges may besmoothed by wet chemical or plasma/RIE etching techniques to mitigatehigh field effects. These process steps form N+ source and drain regions9533 and P− transistor channel region 9534.

As illustrated in FIG. 95I, a gate oxide 9512 may be formed and a gatemetal material 9556 may be deposited. The gate oxide 9512 may be anatomic layer deposited (ALD) gate dielectric that is paired with a workfunction specific gate metal 9556 according to an industry standard ofhigh k metal gate process schemes described previously and targeted foruse in a n-channel RCAT. Additionally, the gate oxide 9512 may be formedwith a low temperature oxide deposition or low temperature microwaveplasma oxidation of the silicon surfaces and then a gate material suchas tungsten or aluminum may be deposited. Then the gate material 9556may be chemically mechanically polished, and the gate electrode 9556′defined by masking and etching.

As illustrated in FIG. 95J, the entire structure may be covered with aLow Temperature Oxide 9552, which may be planarized with chemicalmechanical polishing. Contacts and metal interconnects may be formed bylithography and plasma/RIE etch. The n-RCAT N+ source and drain regions9533, P− transistor channel region 9534, gate dielectric 9512 and gateelectrode 9556′ are shown. The p-RCAT P+ source and drain regions 9526,N− transistor channel region 9528, gate dielectric 9511 and gateelectrode 9554′ are shown. Transistor isolation region 9520, oxide 9552,n-RCAT source contact 9562, gate contact 9564, and drain contact 9566are shown. p-RCAT source contact 9572, gate contact 9574, and draincontact 9576 are shown. The n-RCAT source contact 9562 and drain contact9566 provide electrical coupling to their respective N+ regions 9533.The n-RCAT gate contact 9564 provides electrical coupling to gateelectrode 9556′. The p-RCAT source contact 9572 and drain contact 9576provide electrical coupling to their respective N+ regions 9526. Thep-RCAT gate contact 9574 provides electrical coupling to gate electrode9554′. Contacts (not shown) to P+ doped region 9516, and N− doped region9518 may be made to allow biasing for noise suppression andback-gate/substrate biasing.

Interconnect metallization may then be conventionally formed. The thrulayer via 9560 (not shown) may be formed to electrically couple thecomplementary RCAT layer metallization to the acceptor substrate 9510 atacceptor wafer metal connect pad 9580 (not shown). This flow may enablethe formation of a mono-crystalline silicon n-RCAT and p-RCATconstructed in a single layer transfer of prefabricated wafer sizeddoped layers, which may be formed and connected to the underlyingmulti-metal layer semiconductor device without exposing the underlyingdevices to a high temperature.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 95A through 95J are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the n-RCAT may beprocessed prior to the p-RCAT, or that various etch hard masks may beemployed. Such skilled persons will further appreciate that devicesother than a complementary RCAT may be created with minor variations ofthe process flow, such as, for example, complementary bipolar junctiontransistors, or complementary raised source drain extension transistors,or complementary junction-less transistors, or complementary V-groovetransistors. Many other modifications within the scope of the inventionwill suggest themselves to such skilled persons after reading thisspecification. Thus the invention is to be limited only by the appendedclaims.

An alternative method whereby to build both ‘n’ type and ‘p’ typetransistors on the same layer may be to partially process the firstphase of transistor formation on the donor wafer with normal CMOSprocessing including a ‘dummy gate’, a process known as gate-lasttransistors, or gate replacement process, or replacement gate process.In this embodiment of the present invention, a layer transfer of themono-crystalline silicon may be performed after the dummy gate iscompleted and before the formation of a replacement gate. Processingprior to layer transfer may have no temperature restrictions and theprocessing during and after layer transfer may be limited to lowtemperatures, generally, for example, below 400° C. The dummy gate andthe replacement gate may include various materials such as silicon andsilicon dioxide, or metal and low k materials such as TiAlN and HfO2. Anexample may be the high-k metal gate (HKMG) CMOS transistors that havebeen developed for the 45 nm, 32 nm, 22 nm, and future CMOS generations.Intel and TSMC have shown the advantages of a ‘gate-last’ approach toconstruct high performance HKMG CMOS transistors (C, Auth et al., VLSI2008, pp 128-129 and C. H. Jan et al, 2009 IEDM p. 647).

As illustrated in FIG. 70A, a bulk silicon donor wafer 7000 may beprocessed in the normal state of the art HKMG gate-last manner up to thestep prior to where CMP exposure of the polysilicon dummy gates takesplace. FIG. 70A illustrates a cross section of the bulk silicon donorwafer 7000, the isolation 7002 between transistors, the polysilicon 7004and gate oxide 7005 of both n-type and p-type CMOS dummy gates, theirassociated source and drains 7006 for NMOS and 7007 for PMOS, and theinterlayer dielectric (ILD) 7008. These structures of FIG. 70Aillustrate completion of the first phase of transistor formation. Atthis step, or alternatively just after a CMP of layer 7008 to expose thepolysilicon dummy gates or to planarize the oxide layer 7008 and notexpose the dummy gates, an implant of an atomic species 7010, such as,for example, H+, may prepare the cleaving plane 7012 in the bulk of thedonor substrate for layer transfer suitability, as illustrated in FIG.70B.

The donor wafer 7000 may be now temporarily bonded to carrier substrate7014 at interface 7016 as illustrated in FIG. 70C with a low temperatureprocess that may facilitate a low temperature release. The carriersubstrate 7014 may be a glass substrate to enable state of the artoptical alignment with the acceptor wafer. A temporary bond between thecarrier substrate 7014 and the donor wafer 7000 at interface 7016 may bemade with a polymeric material, such as polyimide DuPont HD3007, whichcan be released at a later step by laser ablation, Ultra-Violetradiation exposure, or thermal decomposition. Alternatively, a temporarybond may be made with uni-polar or bi-polar electrostatic technologysuch as, for example, the Apache tool from Beam Services Inc.

The donor wafer 7000 may then be cleaved at the cleaving plane 7012 andmay be thinned by chemical mechanical polishing (CMP) so that thetransistor isolation 7002 may be exposed at the donor wafer face 7018 asillustrated in FIG. 70D. Alternatively, the CMP could continue to thebottom of the junctions to create a fully depleted SOI layer.

As shown in FIG. 70E, the thin mono-crystalline donor layer face 7018may be prepared for layer transfer by a low temperature oxidation ordeposition of an oxide 7020, and plasma or other surface treatments toprepare the oxide surface 7022 for wafer oxide-to-oxide bonding. Similarsurface preparation may be performed on the 808 acceptor wafer inpreparation for oxide-to-oxide bonding.

A low temperature (for example, less than 400° C.) layer transfer flowmay be performed, as illustrated in FIG. 70E, to transfer the thinnedand first phase of transistor formation pre-processed HKMG silicon layer7001 with attached carrier substrate 7014 to the acceptor wafer 808 witha top metallization comprising metal strips 7024 to act as landing padsfor connection between the circuits formed on the transferred layer withthe underlying circuits—layers 808.

As illustrated in FIG. 70F, the carrier substrate 7014 may then bereleased using a low temperature process such as laser ablation.

The bonded combination of acceptor wafer 808 and HKMG transistor siliconlayer 7001 may now be ready for normal state of the art gate-lasttransistor formation completion. As illustrated in FIG. 70G, the interlayer dielectric 7008 may be chemical mechanically polished to exposethe top of the polysilicon dummy gates. The dummy polysilicon gates maythen be removed by etching and the hi-k gate dielectric 7026 and thePMOS specific work function metal gate 7028 may be deposited. The PMOSwork function metal gate may be removed from the NMOS transistors andthe NMOS specific work function metal gate 7030 may be deposited. Analuminum fill 7032 may be performed on both NMOS and PMOS gates and themetal CMP'ed.

As illustrated in FIG. 70H, a dielectric layer 7032 may be deposited andthe normal gate 7034 and source/drain 7036 contact formation andmetallization may now be performed to connect the transistors on thatmono-crystalline layer and to connect to the acceptor wafer 808 topmetallization strip 7024 with through via 7040 providing connectionthrough the transferred layer from the donor wafer to the acceptorwafer. The top metal layer may be formed to act as the acceptor waferlanding strips for a repeat of the above process flow to stack anotherpreprocessed thin mono-crystalline layer of two-phase formedtransistors. The above process flow may also be utilized to constructgates of other types, such as, for example, doped polysilicon on thermaloxide, doped polysilicon on oxynitride, or other metal gateconfigurations, as ‘dummy gates,’ perform a layer transfer of the thinmono-crystalline layer, replace the gate electrode and gate oxide, andthen proceed with low temperature interconnect processing.Alternatively, SOI wafers with etchback of the bulk silicon to theburied oxide layer may be utilized in place of an ion-cut layer transferscheme.

Alternatively, the carrier substrate 7014 may be a silicon wafer, andinfra-red light and optics could be utilized for alignments. FIGS. 82A-Gare used to illustrate the use of a carrier wafer. FIG. 82A illustratesthe first step of preparing transistors with dummy gates 8202 on firstdonor wafer 8206. The first step may complete the first phase oftransistor formation.

FIG. 82B illustrates forming a cleave line 8208 by implant 8216 ofatomic particles such as H+.

FIG. 82C illustrates permanently bonding the first donor wafer 8206 to asecond donor wafer 8226. The permanent bonding may be oxide-to-oxidewafer bonding as described previously.

FIG. 82D illustrates the second donor wafer 8226 acting as a carrierwafer after cleaving the first donor wafer off; leaving a thin layer8206 with the now buried dummy gate transistors 8202.

FIG. 82E illustrates forming a second cleave line 8218 in the seconddonor wafer 8226 by implant 8246 of atomic species such as, for example,H+.

FIG. 82F illustrates the second layer transfer step to bring the dummygate transistors 8202 ready to be permanently bonded to the house 808.For simplicity of the explanation, the steps of surface layerpreparation done for each of these bonding steps have been left out.

FIG. 82G illustrates the house 808 with the dummy gate transistor 8202on top after cleaving off the second donor wafer and removing the layerson top of the dummy gate transistors. Now the flow may proceed toreplace the dummy gates with the final gates, form the metalinterconnection layers, and continue the 3D fabrication process.Alternatively, SOI wafers with etchback of the bulk silicon to theburied oxide layer may be utilized in place of an ion-cut layer transferscheme.

An interesting alternative is available when using the carrier waferflow. In this flow we can use the two sides of the transferred layer tobuild NMOS on one side and PMOS on the other side. Timing properly thereplacement gate step in such a flow could enable full performancetransistors properly aligned to each other. Compact 3D library cells maybe constructed from this process flow.

As illustrated in FIG. 83A, an SOI (Silicon On Insulator) donor wafer8300 may be processed according to normal state of the art using, e.g.,a HKMG gate-last process, with adjusted thermal cycles to compensate forlater thermal processing, up to the step prior to where CMP exposure ofthe polysilicon dummy gates takes place. Alternatively, the donor wafer8300 may start as a bulk silicon wafer and utilize an oxygenimplantation and thermal anneal to form a buried oxide layer, such asthe SIMOX process (i.e., separation by implantation of oxygen). FIG. 83Aillustrates a cross section of the SOI donor wafer substrate 8300, theburied oxide (i.e., BOX) 8301, the thin silicon layer 8302 of the SOIwafer, the isolation 8303 between transistors, the polysilicon 8304 andgate oxide 8305 of n-type CMOS dummy gates, their associated source anddrains 8306 for NMOS, the NMOS transistor channel 8307, and the NMOSinterlayer dielectric (ILD) 8308. Alternatively, PMOS devices or fullCMOS devices may be constructed at this stage. This stage may completethe first phase of transistor formation.

At this step, or alternatively just after a CMP of layer 8308 to exposethe polysilicon dummy gates or to planarize the oxide layer 8308 and notexpose the dummy gates, an implant of an atomic species 8310, such as,for example, H+, may prepare the cleaving plane 8312 in the bulk of thedonor substrate for layer transfer suitability, as illustrated in FIG.83B.

The SOI donor wafer 8300 may now be permanently bonded to a carrierwafer 8320 that has been prepared with an oxide layer 8316 foroxide-to-oxide bonding to the donor wafer surface 8314 as illustrated inFIG. 83C.

As illustrated in FIG. 83D, the donor wafer 8300 may then be cleaved atthe cleaving plane 8312 and may be thinned by chemical mechanicalpolishing (CMP) and surface 8322 may be prepared for transistorformation.

The donor wafer layer 8300 at surface 8322 may be processed in thenormal state of the art gate last processing to form the PMOStransistors with dummy gates. FIG. 83E illustrates the cross sectionafter the PMOS devices are formed showing the buried oxide (BOX) 8301,the now thin silicon layer 8300 of the SOI substrate, the isolation 8333between transistors, the polysilicon 8334 and gate oxide 8335 of p-typeCMOS dummy gates, their associated source and drains 8336 for PMOS, thePMOS transistor channel 8337, and the PMOS interlayer dielectric (ILD)8338. The PMOS transistors may be precisely aligned at state of the arttolerances to the NMOS transistors due to the shared substrate 8300possessing the same alignment marks. At this step, or alternatively justafter a CMP of layer 8338, the processing flow may proceed to expose thePMOS polysilicon dummy gates or to planarize the oxide layer 8338 andnot expose the dummy gates. Now the wafer could be put into a hightemperature anneal to activate both the NMOS and the PMOS transistors.

Then an implant of an atomic species 8340, such as, for example, H+, mayprepare the cleaving plane 8321 in the bulk of the carrier wafersubstrate 8320 for layer transfer suitability, as illustrated in FIG.83F.

The PMOS transistors may now be ready for normal state of the artgate-last transistor formation completion. As illustrated in FIG. 83G,the inter layer dielectric 8338 may be chemical mechanically polished toexpose the top of the polysilicon dummy gates. The dummy polysilicongates may then be removed by etch and the PMOS hi-k gate dielectric 8340and the PMOS specific work function metal gate 8341 may be deposited. Analuminum fill 8342 may be performed on the PMOS gates and the metalCMP'ed. A dielectric layer 8339 may be deposited and the normal gate8343 and source/drain 8344 contact formation and metallization. The PMOSlayer to NMOS layer via 8347 and metallization may be partially formedas illustrated in FIG. 83G and an oxide layer 8348 may be deposited toprepare for bonding.

The carrier wafer and two sided n/p layer may then be aligned andpermanently bonded to House acceptor wafer 808 with associated metallanding strip 8350 as illustrated in FIG. 83H.

The carrier wafer 8320 may then be cleaved at the cleaving plane 8321and may be thinned by chemical mechanical polishing (CMP) to oxide layer8316 as illustrated in FIG. 831.

The NMOS transistors are now ready for normal state of the art gate-lasttransistor formation completion. As illustrated in FIG. 83J, the NMOSinter layer dielectric 8308 may be chemical mechanically polished toexpose the top of the NMOS polysilicon dummy gates. The dummypolysilicon gates may then be removed by etching and the NMOS hi-k gatedielectric 8360 and the NMOS specific work function metal gate 8361 maybe deposited. An aluminum fill 8362 may be performed on the NMOS gatesand the metal CMP'ed. A dielectric layer 8369 may be deposited and thenormal gate 8363 and source/drain 8364 contacts may be formed andmetalized. The NMOS layer to PMOS layer via 8367 to connect to 8347 andthe metallization of via 8367 may be formed.

As illustrated in FIG. 83K, a dielectric layer 8370 may be deposited.Layer-to-layer through via 8372 may then be aligned, masked, etched, andmetalized to electrically connect to the acceptor wafer 808 andmetal-landing strip 8350. A topmost metal layer of the layer stackillustrated in FIG. 83K may be formed to act as the acceptor waferlanding strips for a repeat of the above process flow to stack anotherpreprocessed thin mono-crystalline layer of transistors. Persons ofordinary skill in the art will appreciate that the illustrations inFIGS. 83A through 83K are exemplary only and are not drawn to scale.Such skilled persons will further appreciate that many variations arepossible such as, for example, the transistor layers on each side of box8301 may comprise full CMOS, or one side may be CMOS and the othern-type MOSFET transistors, logic cells, or other combinations and typesof semiconductor devices. Moreover, SOI wafers with etchback of the bulksilicon to the buried oxide layer may be utilized in place of an ion-cutlayer transfer scheme. Many other modifications within the scope of theinvention will suggest themselves to such skilled persons after readingthis specification. Thus the invention is to be limited only by theappended claims.

FIG. 83L is a top view drawing illustration of a repeating cell 83L00 asa building block for forming gate array, of two NMOS transistors 83L04with shared diffusion 83L05 overlaying ‘face down’ two PMOS transistors83L02 with shared diffusion. The NMOS transistors gates overlay the PMOStransistors gates 83L10 and the overlayed gates are connected to eachother by via 83L12. The Vdd power line 83L06 could run as part of theface down generic structure with connection to the upper layer usingvias 83L20. The diffusion connection 83L08 will be using the face downmetal generic structure 83L17 and brought up by vias 83L14, 83L16,83L18.

FIG. 83L1 is a drawing illustration of the generic cell 83L00 customizedby custom NMOS transistor contacts 83L22, 83L24 and custom metal 83L26to form a double inverter. The Vss power line 83L25 may run on top ofthe NMOS transistors.

FIG. 83L2 is a drawing illustration of the generic cell 83L00 customizedto a NOR function, FIG. 83L3 is a drawing illustration of the genericcell 83L00 customized to a NAND function and FIG. 83L3 is a drawingillustration of the generic cell 83L00 customized to a multiplexerfunction. Accordingly cell 83L00 could be customized to substantiallyprovide the logic functions, such as, for example, NAND and NORfunctions, so a generic gate array using array of cells 83L00 could becustomized with custom contacts vias and metal layers to any logicfunction. Thus, the NMOS, or n-type, transistors may be formed on onelayer and the PMOS, or p-type, transistors may be formed on anotherlayer, and connection paths may be formed between the n-type and p-typetransistors to create Complementary Metal-Oxide-Semiconductor (CMOS)logic cells. Additionally, the n-type and p-type transistors layers mayreside on the first, second, third, or any other of a number of layersin the 3D structure, substantially overlaying the other layer, and anyother previously constructed layer.

Another alternative, with reference to FIG. 70 and description, isillustrated in FIG. 70B-1 whereby the implant of an atomic species 7010,such as, for example, H+, may be screened from the sensitive gate areas7003 by first masking and etching a shield implant stopping layer of adense material 7050, for example 5000 angstroms of Tantalum, and may becombined with 5,000 angstroms of photoresist 7052. This may create asegmented cleave plane 7012 in the bulk of the donor wafer silicon waferand additional polishing may be applied to provide a smooth bondingsurface for layer transfer suitability.

Additional alternatives to the use of an SOI donor wafer may be employedto isolate transistors in the vertical direction. For example, a pnjunction may be formed between the vertically stacked transistors andmay be biased. Also, oxygen ions may be implanted between the verticallystacked transistors and annealed to form a buried oxide layer. Also, asilicon-on-replacement-insulator technique may be utilized for the firstformed dummy transistors wherein a buried SiGe layer is selectivelyetched out and refilled with oxide, thereby creating islands ofelectrically isolated silicon.

An additional alternative to the use of an SOI donor wafer or the use ofion-cut methods to enable a layer transfer of a well-controlled thinlayer of pre-processed layer or layers of semiconductor material,devices, or transistors to the acceptor wafer or substrate isillustrated in FIGS. 150A to C. An additional embodiment of the presentinvention is to form and utilize layer transfer demarcation plugs toprovide an etch-back stop or marker for the controlled thinning of thedonor wafer.

As illustrated in FIG. 150A, a generalized process flow may begin with adonor wafer 15000 that is preprocessed with layers 15002 which mayinclude, for example, conducting, semi-conducting or insulatingmaterials that may be formed by deposition, ion implantation and anneal,oxidation, epitaxial growth, combinations of above, or othersemiconductor processing steps and methods. Additionally, donor wafer15000 may be a fully formed CMOS or other device type wafer, whereinlayers 15002 may include, for example, transistors and metalinterconnect layers. Donor wafer 15000 may be a partially processed CMOSor other device type wafer, wherein layers 15002 may include, forexample, transistors and an interlayer dielectric deposited that may beprocessed just prior to the first contact lithographic step. Layertransfer demarcation plugs (LTDPs) 15030 may be lithographically definedand then plasma/RIE etched to a depth (shown) of approximately the layertransfer demarcation plane 15099. The LTDPs 15030 may also be etched toa depth past the layer transfer demarcation plane 15099 and further intothe donor wafer 15000 or to a depth that is shallower than the layertransfer demarcation plane 15099. The LTDPs 15030 may be filled with anetch-stop material, such as, for example, silicon dioxide, tungsten,heavily doped P+ silicon or polycrystalline silicon, copper, or acombination of etch-stop materials, and planarized with a process suchas, for example, chemical mechanical polishing (CMP) or RIE/plasmaetching. Donor wafer 15000 may be further thinned by CMP. The placementon donor wafer 15000 of the LTDPs 15030 may include, for example, in thescribelines, white spaces in the preformed circuits, or any pattern anddensity for use as electrical or thermal coupling between donor andacceptor layers. The term white spaces may be understood as areas on anintegrated circuit wherein the density of structures above the siliconlayer is small enough, allowing other structures, such as LTDPs, to beplaced with minimal impact to the existing structure's layout positionand organization. The size of the LTDPs 15030 formed on donor wafer15000 may include, for example, diameters of the state of the artprocess via or contact, or may be larger or smaller than the state ofthe art. LTDPs 15030 may be processed before or after layers 15002 areformed. Further processing to complete the devices and interconnectionof layers 15002 on donor wafer 15000 may take place after the LTDPs15030 are formed. Acceptor wafer 15010 may be a preprocessed wafer thathas fully functional circuitry or may be a wafer with previouslytransferred layers, or may be a blank carrier or holder wafer, or otherkinds of substrates and may be called a target wafer. The acceptor wafer15010 and the donor wafer 15000 may be, for example, a bulkmono-crystalline silicon wafer or a Silicon On Insulator (SOI) wafer ora Germanium on Insulator (GeOI) wafer. Acceptor wafer 15010 may havemetal connect pads and acceptor wafer alignment marks as describedpreviously for acceptor wafers with reference to FIG. 8.

Both the donor wafer 15000 and the acceptor wafer 15010 bonding surfaces15001 and 15011 may be prepared for wafer bonding by depositions,polishes, plasma, or wet chemistry treatments to facilitate successfulwafer to wafer bonding.

As illustrated in FIG. 150B, the donor wafer 15000 with layers 15002,LTDPs 15030, and layer transfer demarcation plane 15099 may then beflipped over, aligned and bonded to the acceptor wafer 15010 aspreviously described.

As illustrated in FIG. 150C, the donor wafer 15000 may be thinned toapproximately the layer transfer demarcation plane 15099, leaving aportion of the donor wafer 15000′, LTDPs 15030′ and the pre-processedlayers 15002 aligned and bonded to the acceptor wafer 15010. The donorwafer 15000 may be controllably thinned to the layer transferdemarcation plane 15099 by utilizing the LTDPs 15030 as etch stops oretch stopping indicators. For example, the LTDPs 15030 may besubstantially composed of heavily doped P+ silicon. The thinningprocess, such as CMP with pressure force or optical detection, wet etchwith optical detection, plasma etching with optical detection, ormist/spray etching with optical detection, may incorporate a selectiveetch chemistry, such as, for example, etching agents that etch n− Si orp− Si but do not attack p+ Si doped above 1E20/cm³ include KOH, EDP(ethylenediamine/pyrocatechol/water) and hydrazine, that etches lightlydoped silicon quickly but has a very slow etch rate of heavily doped P+silicon, and may sense the exposed and un-etched LTDPs 15030 as a padpressure force change or optical detection of the exposed and un-etchedLTDPs, and may stop the etch-back processing.

Additionally, for example, the LTDPs 15030 may be substantially composedof a physically dense and hard material, such as, for example, tungstenor diamond-like carbon (DLC). The thinning process, such as CMP withpressure force detection, may sense the hard material of the LTDPs 15030by force pressure changes as the LTDPs 15030 are exposed during theetch-back or thinning processing and may stop the etch-back processing.Additionally, for example, the LTDPs 15030 may be substantially composedof an optically reflective or absorptive material, such as, for example,aluminum, copper, polymers, tungsten, or diamond like carbon (DLC). Thethinning process, such as CMP with optical detection, wet etch withoptical detection, plasma etch with optical detection, or mist/sprayetching with optical detection, may sense the material in the LTDPs15030 by optical detection of color, reflectivity, or wavelengthabsorption changes as the LTDPs 15030 are exposed during the etch-backor thinning processing and may stop the etch-back processing.Additionally, for example, the LTDPs 15030 may be substantially composedof chemically detectable material, such as silicon oxide, polymers, softmetals such as copper or aluminum. The thinning process, such as CMPwith chemical detection, wet etch with chemical detection, RIE/Plasmaetching with chemical detection, or mist/spray etching with chemicaldetection, may sense the dissolution of the LTDPs 15030 material bychemical detection means as the LTDPs 15030 are exposed during theetch-back or thinning processing and may stop the etch-back processing.The chemical detection methods may include, for example, time of flightmass spectrometry, liquid ion chromatography, or spectroscopic methodssuch as infra-red, ultraviolet/visible, or Raman. The thinned surfacemay be smoothed or further thinned by processes described in thispresent invention document. The LTDPs 15030 may be replaced, partiallyor completely, with a conductive material, such as, for example, copper,aluminum, or tungsten, and may be utilized as donor layer to acceptorwafer interconnect.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 150A to 150C are exemplary only and are not drawnto scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the LTDP methods outlinedmay be applied to a variety of layer transfer and 3DIC process flows,including, for example, FIGS. 70, 81, 82, 83, 85 in this application.Moreover, the LTDPs 15030 may not only be utilized as donor wafer layersto acceptor wafer layers electrical interconnect, but may also beutilized as heat conducting paths as a portion of a heat removal systemfor the 3DIC. Further, this LTDP methodology may also be utilized inconcert with the precision alignment technique described in relation toFIG. 111 wherein oxide filled plugs are utilized of large (foralignment) and small (for interconnect) during layer transfer alignmentand bonding processes, and are then the oxide is removed from the LTDPsand the LTDPs are filled with conductive material for layer to layerinterconnect electrical or thermal interconnect. Such skilled personswill further appreciate that the layer transfer demarcation plane 15000and associated etch depth of the LTDPs 15030 may lie within the layers15002, at the transition between layers 15002 and donor wafer 15000, orin the donor wafer 15002 (shown). Many other modifications within thescope of the invention will suggest themselves to such skilled personsafter reading this specification. Thus the invention is to be limitedonly by the appended claims.

An alternative embodiment of the above process flow with reference toFIG. 70 is illustrated in FIGS. 81A to 81F and may provide a face downCMOS planar transistor layer on top of a preprocessed House substrate.The CMOS planar transistors may be fabricated with dummy gates and thecleave plane 7012 may be created in the donor wafer as describedpreviously and illustrated in FIGS. 70A and 70B. Then the dummy gatesmay be replaced as described previously and illustrated in FIG. 81A.

The contact and metallization steps may be performed as illustrated inFIG. 81B to allow future connections to the transistors once they areface down.

The face 8102 of donor wafer 8100 may be prepared for bonding bydeposition of an oxide 8104, and plasma or other surface treatments toprepare the oxide surface 8106 for wafer-to-wafer oxide-to-oxide bondingas illustrated in FIG. 81C.

Similar surface preparation may be performed on the 808 acceptor waferin preparation for the oxide-to-oxide bonding. Now a low temperature(e.g., less than 400° C.) layer transfer flow may be performed, asillustrated in FIG. 81D, to transfer the prepared donor wafer 8100 withtop surface 8106 to the acceptor wafer 808. Acceptor wafer 808 may bepreprocessed with transistor circuitry and metal interconnect and mayhave a top metallization comprising metal strips 8124 to act as landingpads for connection between the circuits formed on the transferred layerwith the underlying circuit layers in house 808. For FIGS. 81D to 81F,an additional STI (shallow trench isolation) isolation 8130 without via7040 may be added to the illustration.

The donor wafer 8100 may then be cleaved at the cleaving plane 7012 andmay be thinned by chemical mechanical polishing (CMP) so that thetransistor isolations 7002 and 8130 may be exposed as illustrated inFIG. 81E. Alternatively, the CMP could continue to the bottom of thejunctions to create a fully depleted SOI layer.

As illustrated in FIG. 81F, a low-temperature oxide or low-k dielectric8136 may be deposited and planarized. The through via 8128 to house 808acceptor wafer landing strip 8124 and contact 8140 to thru via 7040 maybe etched, metalized, and connected by metal line 8150 to provideelectrical connection from the donor wafer transistors to the acceptorwafer. The length of landing strips 8124 may be at least the repeatwidth W plus margin per the proper via design rules as shown in FIGS. 32and 33A. The landing zone strip extension for proper via design rulesmay include angular misalignment of the wafer-to-wafer bonding that isnot compensated for by the stepper overlay algorithms, and may includeuncompensated donor wafer bow and warp.

The face down flow has some advantages such as, for example, enablingdouble gate transistors, back biased transistors, or access to thefloating body in memory applications. For example, a back gate for adouble gate transistor may be constructed as illustrated in FIG. 81E-1.A low temperature gate oxide 8160 with gate material 8162 may be grownor deposited and defined by lithographic and etch processes as describedpreviously.

The metal hookup may be constructed as illustrated in FIG. 81F-1.

As illustrated in FIG. 81F-2, fully depleted SOI transistors withjunctions 8170 and 8171 may be alternatively constructed in this flow asdescribed in respect to CMP thinning illustrated in FIG. 81E.

An alternative embodiment of the above double gate process flow that mayprovide a back gate in a face-up flow is illustrated in FIGS. 85A to 85Ewith reference to FIG. 70. The CMOS planar transistors may be fabricatedwith the dummy gates and the cleave plane 7012 may be created in thedonor wafer, bulk or SOT, as described and illustrated in FIGS. 70A and70B. The donor wafer may be attached either permanently or temporarilyto the carrier substrate as described and illustrated in FIG. 70C andthen cleaved and thinned to the STI 7002 as shown in FIG. 70D.Alternatively, the CMP could continue to the bottom of the junctions tocreate a fully depleted SOI layer.

A second gate oxide 8502 may be grown or deposited as illustrated inFIG. 85A and a gate material 8504 may be deposited. The gate oxide 8502and gate material 8504 may be formed with low temperature (e.g., lessthan 400° C.) materials and processing, such as previously described TELSPA gate oxide and amorphous silicon, ALD techniques, or hi-k metal gatestack (HKMG), or may be formed with a higher temperature gate oxide oroxynitride and doped polysilicon if the carrier substrate bond ispermanent and the existing planar transistor dopant movement isaccounted for.

The gate stack 8506 may be defined, a dielectric 8508 may be depositedand planarized, and then local contacts 8510 and layer to layer contacts8512 and metallization 8516 may be formed as illustrated in FIG. 85B.

As shown in FIG. 85C, the thin mono-crystalline donor and carriersubstrate stack may be prepared for layer transfer by methods previouslydescribed including oxide layer 8520. Similar surface preparation may beperformed on house 808 acceptor wafer in preparation for oxide-to-oxidebonding. Now a low temperature (e.g., less than 400° C.) layer transferflow may be performed, as illustrated in FIG. 85C, to transfer thethinned and first-phase-transistor-formation-pre-processed HKMG siliconlayer 7001 and back gates 8506 with attached carrier substrate 7014 tothe acceptor wafer 808. The acceptor wafer 808 may have a topmetallization comprising metal strips 8124 to act as landing pads forconnection between the circuits formed on the transferred layer with theunderlying circuit layers 808.

As illustrated in FIG. 85D, the carrier substrate 7014 may then bereleased at surface 7016 as previously described.

The bonded combination of acceptor wafer 808 and HKMG transistor siliconlayer 7001 may now be ready for normal state of the art gate-lasttransistor formation completion as illustrated in FIG. 85E andconnection to the acceptor wafer House 808 thru layer to layer via 7040.The top transistor 8550 may be back gated by connecting the top gate tothe bottom gate thru gate contact 7034 to metal line 8536 and to contact8522 to connect to the donor wafer layer through layer contact 8512. Thetop transistor 8552 may be back biased by connecting metal line 8516 toa back bias circuit that may be in the top transistor level or in theHouse 808. Moreover, SOI wafers with etchback of the bulk silicon to theburied oxide layer may be utilized in place of an ion-cut layer transferscheme.

The present invention may overcome the challenge of forming these planartransistors aligned to the underlying layers 808 as described inassociation with FIGS. 71 to 79 and FIGS. 30 to 33. The general flow maybe applied to the transistor constructions described before as relatingto FIGS. 70 A-H. In one embodiment, the donor wafer 3000 may bepre-processed to build not just one transistor type but both types bycomprising alternating parallel rows that are the die width plus maximumdonor wafer to acceptor wafer misalignment in length. Alternatively, therows may be made wafer long for the first phase of transistor formationof ‘n’ type 3004 and ‘p’ type 3006 transistors as illustrated in FIG.30. FIG. 30 may also include a four cardinal directions 3040 indicator,which will be used through FIGS. 71 to 78. As shown in the blown upprojection 3002, the width of the n-type rows 3004 is Wn and the widthof the p-type rows 3006 is Wp and their sum W 3008 is the width of therepeating pattern. The rows traverse from East to West and thealternating pattern repeats substantially all the way across the waferfrom North to South. Wn and Wp may be set for the minimum width of thecorresponding transistor, n-type transistor and p-type transistorrespectively, plus its isolation in the selected process node. The wafer3000 may also have an alignment mark 3020 on the same layers of thedonor wafer as the n 3004 and p 3006 rows and accordingly may be usedlater to properly align additional patterning and processing steps tothe n 3004 and p 3006 rows.

As illustrated in FIG. 71, the width of the p type transistor row widthrepeat Wp 7106 may be composed of two transistor isolations 7110 ofwidth 2 F each, plus a transistor source 7112 of width 2.5 F, a PMOSgate 7113 of width F, and a transistor drain 7114 of width 2.5 F. Thetotal Wp may be 10 F, where F is 2 times lambda, the minimum designrule. The width of the n type transistor row width repeat Wn 7104 may becomposed of two transistor isolations 7110 of width 2 F each, plus atransistor source 7116 of width 2.5 F, a NMOS gate 7117 of width F, anda transistor drain 7118 of width 2.5 F. The total Wn may be 10 F and thetotal repeat W 7108 may be 20 F.

The donor wafer layer 3000L, now thinned and thefirst-phase-transistor-formation pre-processed HKMG silicon layer 7001with the attached carrier substrate 7014 completed as describedpreviously in relation to FIG. 70E, may be placed on top of the acceptorwafer 3100 as illustrated in FIG. 31. The state of the art alignmentmethods allow for very good angular alignment of this bonding step butit is difficult to achieve a better than approximately 1 micron positionalignment. FIG. 31 illustrates the acceptor wafer 3100 with itscorresponding alignment mark 3120 and the transferred layer 3000L of thedonor wafer with its corresponding alignment mark 3020. The misalignmentin the East-West direction is DX 3124 and the misalignment in theNorth-South direction is DY 3122. These alignment marks 3120 and 3020may be placed in only a few locations on each wafer, or within each stepfield, or within each die, or within each repeat W. The alignmentapproach involving residue Rdy 3202 and the landing zone stripes 33A04and 33B04 as described previously in respect to FIGS. 32, 33A and 33Bmay be utilized to improve the density and reliability of the electricalconnection from the transferred donor wafer layer to the acceptor wafer.

The low temperature post layer transfer process flow for the donor waferlayout with gates parallel to the source and drains as shown in FIG. 71is illustrated in FIGS. 72A to 72F.

FIG. 72A illustrates the top view and cross-sectional view of the waferafter layer transfer of the first phase of transistor formation, layertransfer & bonding of the thin mono-crystalline preprocessed donor layerto the acceptor wafer, and release of the bonded structure from thecarrier substrate, as previously described up to and including FIG. 70F.

The interlayer dielectric (ILD) 7008 may be chemical mechanical polished(CMP'd) to expose the top of the dummy polysilicon and thelayer-to-layer via 7040 may be etched, metal filled, and CMP'd flat asillustrated in FIG. 72B.

The long rows of pre-formed transistors may be etched into lengths orsegments by forming isolation regions 7202 as illustrated in FIG. 72C. Alow temperature oxidation may be performed to repair damage to thetransistor edge and the regions 7202 may be filled with a dielectric andCMP'd flat so to provide isolation between transistor segments.

Alternatively, regions 7202 may be selectively opened and filled for thePMOS and NMOS transistors separately to provide compressive or tensilestress enhancement to the transistor channels for carrier mobilityenhancement.

The polysilicon 7004 and oxide 7005 dummy gates may now be etched out toprovide some gate overlap between the isolation 7202 edge and the normalreplacement gate deposition of high-k dielectric 7026, PMOS metal gate7028 and NMOS metal gate 7030. In addition, aluminum overfill 7032 maybe performed. The CMP of the Aluminum 7032 may be performed to planarizethe surface for the gate definition as illustrated in FIG. 72D.

The replacement gates 7215 may be patterned and etched as illustrated inFIG. 72E and may provide a gate contact landing area 7218.

An interlayer dielectric may be deposited and planarized with CMP, andnormal contact formation and metallization may be performed to make gate7220, source 7222, drain 7224, and interlayer via 7240 connections asillustrated in FIG. 72F.

In an alternative embodiment, the donor wafer 7000 may be pre-processedfor the first phase of transistor formation to build n and p type dummytransistors comprising repeated patterns in both directions. FIGS. 73,74, 75 include a four cardinal directions 3040 indicator, which may beused to assist the explanation. As illustrated in the blown-upprojection 7302 in FIG. 73, the width Wy 7304 corresponds to therepeating pattern rows that may traverse the acceptor die East to Westwidth plus the maximum donor wafer to acceptor wafer misalignmentlength, or alternatively traverse the length of the donor wafer fromEast to West, and the repeats may extend substantially all the wayacross the wafer from North to South. Similarly, the width Wx 7306corresponds to the repeating pattern rows that may traverse the acceptordie North to South width plus the maximum donor wafer to acceptor wafermisalignment length, or alternatively traverse the length of the donorwafer from North to South, and the repeats may extend substantially allthe way across the wafer from East to West. The donor wafer 7000 mayalso have an alignment mark 3020 on the same layers of the donor waferas the Wx 7306 and Wy 7304 repeating patterns rows. Accordingly,alignment mark 3020 may be used later to properly align additionalpatterning and processing steps to said rows.

The donor wafer layer 3000L, now thinned and comprising the first phaseof transistor formation pre-processed HKMG silicon layer 7001 withattached carrier substrate 7014 completed as described previously inrelation to FIG. 70E, may be placed on top of the acceptor wafer 3100 asillustrated in FIG. 31. The state of the art alignment may allow forvery good angular alignment of this bonding step but it is difficult toachieve a better than approximately 1 micron position alignment. FIG. 31illustrates the acceptor wafer 3100 with its corresponding alignmentmark 3120 and the transferred layer 3000L of the donor wafer with itscorresponding alignment mark 3020. The misalignment in the East-Westdirection is DX 3124 and the misalignment in the North-South directionis DY 3122. These alignment marks may be placed in only a few locationson each wafer, or within each step field, or within each die, or withineach repeat W.

The proposed structure, illustrated in FIG. 74, comprise repeatingpatterns in both the North-South and East-West direction of alternatingrows of parallel transistor bands. The advantage of the proposedstructure is that the transistor and the processing could be similar tothe acceptor wafer processing, thereby significantly reducing thedevelopment cost of 3D integrated devices. Accordingly the effectivealignment uncertainty may be reduced to Wy 7304 in the North to Southdirection and Wx 7306 in the West to East direction. Accordingly, thealignment residue Rdy 3202 (remainder of DY modulo Wy, 0<=Rdy<Wy) in theNorth to South direction could be calculated. Accordingly, theNorth-South direction alignment may be to the underlying alignment mark3120 offset by Rdy 3202 to properly align to the nearest Wy. Similarly,the effective alignment uncertainty may be reduced to Wx 7306 in theEast to West direction. The alignment residue Rdx 3708 (remainder of DXmodulo Wx, 0<=Rdx<Wx) in the West to East direction could be calculatedin a manner similar to that of Rdy 3202. Likewise, the East-Westdirection alignment may be performed to the underlying alignment mark3120 offset by Rdx 7308 to properly align to the nearest Wx.

Each wafer to be processed according to this flow may have at least onespecific Rdx 7308 and Rdy 3202 which may be subject to the actualmisalignment DX 3124 and DY 3122 and Wx and Wy. The masks used forpatterning the various circuit patterns may be pre-designed andfabricated and remain the same for substantially all wafers (processedfor the same end-device) regardless of the actual wafer to wafermisalignment. In order to allow the connection between structures on thedonor layer 7001 and the underlying acceptor wafer 808, the underlyingwafer 808 may be designed to have a landing zone rectangle 7504extending North-South of length Wy 7304 plus any extension necessary forthe via design rules, and extending East-West of length Wx 7306 plus anyextension required for the via design rules, as illustrated in FIG. 75.The landing zone rectangle extension for via design rules may alsoinclude angular misalignment of the wafer-to-wafer bonding notcompensated by the stepper overlay algorithms, and may includeuncompensated donor wafer bow and warp. The rectangle landing zone 7504may be part of the acceptor wafer 808 and may be accordingly aligned toits alignment mark 3120. Through via 7502 going down and being part ofthe donor layer 7001 pattern may be aligned to the underlying alignmentmark 3120 by offsets Rdx 7308 and Rdy 3202 respectively, providingconnections to the landing zone 7504. Through via 7502 may be drawn inthe database (not shown) so that it is positioned approximately at thecenter of the rectangle landing zone 7504, and, hence, may be away fromthe ends of the rectangle landing zone 7504 at distances greater thanapproximately the nominal layer to layer misalignment margin.

In an alternative embodiment, the rectangular landing zone 7504 inacceptor substrate 808 may be replaced by a landing strip 77A04 in theacceptor wafer and an orthogonal landing strip 77A06 in the donor layeras illustrated in FIG. 77. Through via 77A02 going down and being partof the donor layer 7001 pattern may be aligned to the underlyingalignment mark 3120 by offsets Rdx 7308 and Rdy 3202 respectively,providing connections to the landing strip 77A06. Through via 77A02 maybe drawn in the database (not shown) so that it is positionedapproximately at the center of landing strip 77A04 and landing strip77A06, and, hence, may be away from the ends of strip 77A04 and strip77A06 at distances greater than approximately the nominal layer to layermisalignment margin.

FIG. 76 illustrates a repeating pattern in both the North-South andEast-West direction. This repeating pattern may be a repeating patternof transistors, of which each transistor has gate 7622, forming a bandof transistors along the East-West axis. The repeating pattern in theNorth-South direction may comprise parallel bands of transistors, ofwhich each transistor has active area 7612 or 7614. The transistors mayhave their gates 7622 fully defined. The structure may therefore berepeating in East-West with repetitions of Wx 7306. In the North-Southdirection the structure may repeat every Wy 7304. The width Wv 7602 ofthe layer to layer via channel 7618 may be 5 F, and the width of the ntype transistor row width repeat Wn 7604 may be composed of twotransistor isolations 7610 of 3 F width and shared isolation region 7616of 1 F width, plus a transistor active area 7614 of width 2.5 F. Thewidth of the p type transistor row width repeat Wp 7606 may be composedof two transistor isolations 7610 of 3 F width and shared 7616 of 1 F,plus a transistor active area 7612 of width 2.5 F. The total Wy 7304 maybe 18 F, the addition of Wv+Wn+Wp, where F is two times lambda, theminimum design rule. The gates 7622 may be of width F and spaced 4 Fapart from each other in the East-West direction. The East-West repeatwidth Wx 7306 may be 5 F. Adjacent transistors in the East-Westdirection may be electrically isolated from each other by biasing thegate in-between to the appropriate off state; i.e., grounded gate forNMOS and Vdd gate for PMOS.

The donor wafer layer 3000L, now thinned and comprising thefirst-phase-transistor-formation pre-processed HKMG silicon layer 7001with attached carrier substrate 7014 completed as described previouslyin relation to FIG. 70E, may be placed on top of the acceptor wafer 3100as illustrated in FIG. 31. The DX 3124 and DY 3122 misalignment and, asdescribed previously, the associated Rdx 7308 and Rdy 3202 may becalculated. The connection between structures on the donor layer 7001and the underlying wafer 808, may be designed to have a landing strip77A04 going North-South of length Wy 7304 plus any extension necessaryfor the via design rules, as illustrated in FIG. 77A. The landing stripextension for via design rules may include angular misalignment of thewafer to wafer bonding not compensated for by the stepper overlayalgorithms, and may include uncompensated donor wafer bow and warp. Thestrip 77A04 may be part of the wafer 808 and may be accordingly alignedto its alignment mark 3120. The landing strip 77A06 may be part of thedonor wafer layers and may be oriented in parallel to the transistorbands and accordingly going East-West. Landing strip 77A06 may bealigned to the main wafer alignment mark 3120 with offsets of Rdx andRdy (i.e., equivalent to alignment to donor wafer alignment mark 3020).Through via 77A02 connecting these two landing strips 77A04 and 77A06may be part of a top layer 7001 pattern. The via 77A02 may be aligned tothe main wafer 808 alignment mark in the West-East direction and to themain wafer alignment mark 3120 with Rdy offset in the North-Southdirection.

Alternatively, the repeating pattern of continuous diffusion sea ofgates described in FIG. 76 may have an enlarged Wv 7802 for multiplerows of landing strips 77A06 as illustrated in FIG. 78A. The width Wv7802 of the layer-to-layer via channel 7618 may be 10 F, and the totalWy 7804 North-South pattern repeat may be 23 F.

In an alternative embodiment, the gates 7622B may be repeated in theEast to West direction as pairs with an additional repeat of isolations7810 as illustrated in FIG. 78B. This repeating pattern of transistors,of which each transistor has gate 7622B, may form a band of transistorsalong the East-West axis. The repeating pattern in the North-Southdirection comprises parallel bands of these transistors, of which eachtransistor has active area 7612 or 7614. The East-West pattern repeatwidth Wx 7806 may be 14 F and the length of the donor wafer landingstrips 77A06 may be designed of length Wx 7806 plus any extensionnecessary by design rules as described previously. The donor waferlanding strip 77A06 may be oriented parallel to the transistor bands andaccordingly going East-West.

FIG. 78C illustrates a section of a Gate Array terrain with a repeatingtransistor cell structure. The cell is similar to the one of FIG. 78Bwherein the respective gates of the N transistors are connected to thegates of the P transistors. FIG. 78C illustrates an implementation ofbasic logic cells: Inv, NAND, NOR, MUX.

Alternatively, to increase the density of thru layer via connections inthe donor wafer layer to layer via channel, the donor landing strip77A06 may be designed to be less than Wx 7306 in length by utilizingincreases 7900 in the width of the landing strip in the House 77A04 andoffsetting the through layer via 77A02 properly as illustrated in FIG.79. The landing strips 77A04 and 77A06 may be aligned as describedpreviously. Via 77A02 may be aligned to the main wafer alignment mark3120 with Rdy offset in the North-South direction, and in the East-Westdirection to the acceptor wafer 808 alignment mark 3120 as describedpreviously plus an additional shift towards East. The offset size may beequal to the reduction of the donor wafer landing strip 77A06.

In an additional embodiment, a block of a non-repeating pattern devicestructures may be prepared on a donor wafer and layer transferred usingthe above described techniques. This donor wafer of non-repeatingpattern device structure may be a memory block of DRAM, or a block ofInput-Output circuits, or any other block. A general connectivitystructure 8002 may be used to connect the donor wafer non-repeatingpattern device structure 8004 to the acceptor wafer-house wafer die8000.

House 808 wafer die 8000 is illustrated in FIG. 80. The connectivitystructure 8002 may be drawn inside or outside of the non-repeatingstructure 8004. Mx 8006 may be the maximum donor wafer to acceptor wafer8000 misalignment plus any extension necessary by design rules asdescribed previously in the East-West direction and My 8008 may be themaximum donor wafer to acceptor wafer misalignment plus any extensionnecessary by design rules as described previously in the North-Southdirection from the layer transfer process. Mx 8006 and My 8008 may alsoinclude incremental misalignment resulting from the angular misalignmentof the wafer to wafer bonding not compensated for by the stepper overlayalgorithms, and may include uncompensated donor wafer bow and warp. Theacceptor wafer North-South landing strip 8010 may have a length of My8008 aligned to the acceptor wafer alignment mark 3120. The donor waferEast-West landing strip 8011 may have a length of Mx 8006 aligned to thedonor wafer alignment mark 3020. The through layer via 8012 connectingthem may be aligned to the acceptor wafer alignment mark 3120 in theEast West direction and to the donor wafer alignment mark 3020 in theNorth-South direction. For the purpose of illustration, the lower metallanding strip of the donor wafer was oriented East-West and the uppermetal landing strip of the acceptor was oriented North-South. Theorientation of the landing strips could be exchanged. Through layer via8012 may be drawn in the database (not shown) so that it is positionedapproximately at the center of landing strip 8010 and landing strip8011, and, hence, may be away from the ends of strip 8010 and strip 8011at distances greater than approximately the nominal layer to layermisalignment margin.

The donor wafer may comprise sections of repeating device structureelements such as those illustrated in FIG. 76 and FIG. 78B incombination with device structure elements that do not repeat. These twoelements, one repeating and the other non-repeating, would be patternedseparately since the non-repeating elements pattern should be aligned tothe donor wafer alignment mark 3020, while the pattern for the repeatingelements would be aligned to the acceptor wafer alignment mark 3120 withan offset (Rdx & Rdy) as was described previously. Accordingly, avariation of the general connectivity structure illustrated in FIG. 80could be used to connect between to these two elements. The East-Westlanding strips 8011 could be aligned to the donor wafer alignment marks3020 together with the non-repeating elements and the North-Southlanding strips 8010 would be aligned to the acceptor wafer alignmentmark 3120 with the offset together with the repeating elements pattern.The vias 8012 connecting these strips would need to be aligned in theNorth-South direction to the donor wafer alignment marks 3020 and in theEast-West direction to the acceptor wafer alignment mark 3120 with theoffset.

Persons of ordinary skill in the art will appreciate that theillustrations in FIG. 80 are exemplary only and are not drawn to scale.Such skilled persons will further appreciate that many variations arepossible such as, for example, the donor wafer may include onlynon-repeating pattern structures and thus may be connected to theacceptor wafer by acceptor and donor metal landing strips 8010 and 8011of length Mx 8006 and My 8008 and vias 8012 by aligning, which mayinclude adjustments such as, for example, wafer bow, mask runout, andalignment variation, the donor wafer alignment marks to the acceptorwafer alignment marks. Moreover, these alignment schemes for 3DIC may beutilized by many of the device process flows described in this presentinvention. Furthermore, the landing strip directions East-West andNorth-South may be swapped between acceptor and donor wafers. Further,the landing strips may be designed off-orthogonal with respect to eachother, or may be designed to run in other compass directions thanNorth-South and East-West, or both off-orthogonal and off-North-SouthEast-West compass directions. Many other modifications within the scopeof the invention will suggest themselves to such skilled persons afterreading this specification. Thus the invention is to be limited only bythe appended claims.

The above flows, whether single type transistor donor wafer orcomplementary type transistor donor wafer, could be repeated multipletimes to build a multi-level 3D monolithic integrated system. Theseflows could also provide a mix of device technologies in a monolithic 3Dmanner. For example, device I/O or analog circuitry such as, forexample, phase-locked loops (PLL), clock distribution, or RF circuitscould be integrated with CMOS logic circuits via layer transfer, orbipolar circuits could be integrated with CMOS logic circuits, or analogdevices could be integrated with logic, and so on. Prior art showsalternative technologies of constructing 3D devices. The most commontechnologies are, either using thin film transistors (TFT) to constructa monolithic 3D device, or stacking prefabricated wafers and then usinga through silicon via (TSV) to connect the prefabricated wafers. The TFTapproach is limited by the performance of thin film transistors whilethe stacking approach is limited by the relatively large lateral size ofthe TSV via (on the order of a few microns) due to the relatively largethickness of the 3D layer (about 60 microns) and accordingly therelatively low density of the through silicon vias connecting them.According to many embodiments of the present invention that construct 3DIC based on layer transfer techniques, the transferred layer may be athin layer of less than 0.4 micron. This 3D IC with transferred layeraccording to some embodiments of the present invention is in sharpcontrast to TSV based 3D ICs in the prior art where the layers connectedby TSV are more than 5 microns thick and in most cases more than 50microns thick.

The alternative process flows presented in FIGS. 20 to 35, 40, 54 to 61,and 65 to 94 provides true monolithic 3D integrated circuits. It allowsthe use of layers of single crystal silicon transistors with the abilityto have the upper transistors aligned to the underlying circuits as wellas those layers aligned each to other and only limited by the Steppercapabilities. Similarly the contact pitch between the upper transistorsand the underlying circuits is compatible with the contact pitch of theunderlying layers. While in the best current stacking approach the stackwafers are a few microns thick, the alternative process flow presentedin FIGS. 20 to 35, 40, 54 to 61, and 65 to 94 suggests very thin layersof typically 100 nm, but recent work has demonstrated layersapproximately 20 nm thin.

Accordingly the presented alternatives allow for true monolithic 3Ddevices. This monolithic 3D technology provides the ability to integratewith full density, and to be scaled to tighter features, at the samepace as the semiconductor industry.

Additionally, true monolithic 3D devices allow the formation of varioussub-circuit structures in a spatially efficient configuration withhigher performance than 2D equivalent structures. Illustrated below aresome examples of how a 3D ‘library’ of cells may be constructed in thetrue monolithic 3D fashion.

FIG. 42 illustrates a typical 2D CMOS inverter layout and schematicdiagram where the NMOS transistor 4202 and the PMOS transistor 4204 arelaid out side by side and are in differently doped wells. The NMOSsource 4206 is typically grounded, the NMOS and PMOS drains 4208 areelectrically tied together, the NMOS & PMOS gates 4210 are electricallytied together, and the PMOS 4207 source is tied to +Vdd. The structurebuilt in 3D described below will take advantage of these connections inthe 3rd dimension.

An acceptor wafer is preprocessed as illustrated in FIG. 43A. A heavilydoped N single crystal silicon wafer 4300 may be implanted with a heavydose of N+ species, and annealed to create an even lower resistivitylayer 4302. Alternatively, a high temperature resistant metal such asTungsten may be added as a low resistance interconnect layer, as a sheetlayer or as a defined geometry metallization. An oxide 4304 is grown ordeposited to prepare the wafer for bonding. A donor wafer ispreprocessed to prepare for layer transfer as illustrated in FIG. 43B.FIG. 43B is a drawing illustration of the pre-processed donor wafer usedfor a layer transfer. A P− wafer 4310 is processed to make it ready fora layer transfer by a deposition or growth of an oxide 4312, surfaceplasma treatments, and by an implant of an atomic species such as H+preparing the SmartCut cleaving plane 4314. Now a layer-transfer-flowmay be performed to transfer the pre-processed single crystal silicondonor wafer on top of the acceptor wafer as illustrated in FIG. 43C. Thecleaved surface 4316 may or may not be smoothed by a combination of CMP,chemical polish, and epitaxial (EPI) smoothing techniques.

A process flow to create devices and interconnect to build the 3Dlibrary is illustrated in FIGS. 44A to G. As illustrated in FIG. 44A, apolish stop layer 4404, such as silicon nitride or amorphous carbon, maybe deposited after a protecting oxide layer 4402. The NMOS source toground connection 4406 is masked and etched to contact the heavily dopedN+ layer 4302 that serves as a ground plane. This may be done at typicalcontact layer size and precision. For the sake of clarity, the two oxidelayers, 4304 from the acceptor and 4312 from the donor wafer, arecombined and designated as 4400. The NMOS source to ground connection4406 is filled with a deposition of heavily doped polysilicon oramorphous silicon, or a high melting point metal such as tungsten, andthen chemically mechanically polished as illustrated in FIG. 44B to thelevel of the protecting oxide layer 4404.

Now a standard NMOS transistor formation process flow is performed, withtwo exceptions. First, no photolithographic masking steps are used foran implant step that differentiates NMOS and PMOS devices, as only theNMOS devices are being formed now. Second, high temperature anneal stepsmay or may not be done during the NMOS formation, as some orsubstantially all of the necessary anneals can be done after the PMOSformation described later. A typical shallow trench (STI) isolationregion 4410 is formed between the eventual NMOS transistors by masking,plasma etching of the unmasked regions of P− layer 4301 to the oxidelayer 4400, stripping the masking layer, depositing a gap-fill oxide,and chemical mechanically polishing the gap-fill oxide flat asillustrated in FIG. 44C. Threshold adjust implants may or may not beperformed at this time. The silicon surface is cleaned of remainingoxide with an HF (Hydrofluoric Acid) etch.

A gate oxide 4411 is thermally grown and doped polysilicon is depositedto form the gate stack. The gate stack is lithographically defined andetched, creating NMOS gates 4412 and the poly on STI interconnect 4414as illustrated in FIG. 44D. Alternatively, a high-k metal gate processsequence may be utilized at this stage to form the gate stacks 4412 andinterconnect over STI 4414. Gate stack self-aligned LDD (Lightly DopedDrain) and halo punch-thru implants may be performed at this time toadjust junction and transistor breakdown characteristics.

FIG. 44E illustrates a typical spacer deposition of oxide and nitrideand a subsequent etchback, to form implant offset spacers 4416 on thegate stacks and then a self-aligned N+ source and drain implant isperformed to create the NMOS transistor source and drain 4418. Hightemperature anneal steps may or may not be done at this time to activatethe implants and set initial junction depths. A self-aligned silicidemay then be formed. Additionally, one or more metal interconnect layerswith associated contacts and vias (not shown) may be constructedutilizing standard semiconductor manufacturing processes. The metallayer may be constructed at lower temperature using such metals asCopper or Aluminum, or may be constructed with refractory metals such asTungsten to provide high temperature utility at greater than 400 degreesCentigrade. A thick oxide 4420 may be deposited as illustrated in FIG.44F and CMP'd (chemical mechanically polished) flat. The wafer surface4422 may be treated with a plasma activation in preparation to be anacceptor wafer for the next layer transfer.

A donor wafer to create PMOS devices is preprocessed to prepare forlayer transfer as illustrated in FIG. 45A. An N− wafer 4502 is processedto make it ready for a layer transfer by a deposition or growth of anoxide 4504, surface plasma treatments, and by an implant of an atomicspecies, such as H+, preparing the SmartCut cleaving plane 4506.

Now a layer-transfer-flow may be performed to transfer the pre-processedsingle crystal silicon donor wafer on top of the acceptor wafer asillustrated in FIG. 45B, bonding the acceptor wafer oxide 4420 to thedonor wafer oxide 4504. To optimize the PMOS mobility, the donor wafermay be rotated 90 degrees with respect to the acceptor wafer as part ofthe bonding process to facilitate creation of the PMOS channel in the<110> silicon plane direction. The cleaved surface 4508 may or may notbe smoothed by a combination of CMP, chemical polish, and epitaxial(EPI) smoothing techniques.

For the sake of clarity, the two oxide layers, 4420 from the acceptorand 4504 from the donor wafer, are combined and designated as 4500. Nowa standard PMOS transistor formation process flow is performed, with oneexception. No photolithographic masking steps are used for the implantsteps that differentiate NMOS and PMOS devices, as only the PMOS devicesare being formed now. An advantage of this 3D cell structure is theindependent formation of the PMOS transistors and the NMOS transistors.Therefore, each transistor formation may be optimized independently.This may be accomplished by the independent selection of the crystalorientation, various stress materials and techniques, such as, forexample, doping profiles, material thicknesses and compositions,temperature cycles, and so forth.

A polishing stop layer, such as silicon nitride or amorphous carbon, maybe deposited after a protecting oxide layer 4510. A typical shallowtrench (STI) isolation region 4512 is formed between the eventual PMOStransistors by lithographic definition, plasma etching to the oxidelayer 4500, depositing a gap-fill oxide, and chemical mechanicallypolishing flat as illustrated in FIG. 45C. Threshold adjust implants mayor may not be performed at this time.

The silicon surface is cleaned of remaining oxide with an HF(Hydrofluoric Acid) etch. A gate oxide 4514 is thermally grown and dopedpolysilicon is deposited to form the gate stack. The gate stack islithographically defined and etched, creating PMOS gates 4516 and thepoly on STI interconnect 4518 as illustrated in FIG. 45D. Alternatively,a high-k metal gate process sequence may be utilized at this stage toform the gate stacks 4516 and interconnect over STI 4518. Gate stackself-aligned LDD (Lightly Doped Drain) and halo punch-thru implants maybe performed at this time to adjust junction and transistor breakdowncharacteristics.

FIG. 45E illustrates a typical spacer deposition of oxide and nitrideand a subsequent etchback, to form implant offset spacers 4520 on thegate stacks and then a self-aligned P+ source and drain implant isperformed to create the PMOS transistor source and drain regions 4522.Thermal anneals to activate implants and set junctions in both the PMOSand NMOS devices may be performed with RTA (Rapid Thermal Anneal) orfurnace thermal exposures. Alternatively, laser annealing may beutilized after the NMOS and PMOS sources and drain implants to activateimplants and set the junctions. Optically absorptive and reflectivelayers as described previously may be employed to anneal implants andactivate junctions.

A thick oxide 4524 is deposited as illustrated in FIG. 45F and CMP'ed(chemical mechanically polished) flat.

FIG. 45G illustrates the formation of the three groups of eightinterlayer contacts. An etch stop and polishing stop layer or layers4530 may be deposited, such as silicon nitride or amorphous carbon.First, the deepest contact 4532 to the N+ ground plane layer 4302, aswell as the NMOS drain only contact 4540 and the NMOS only gate on STIcontact 4546 are masked and etched in a first contact step. Then theNMOS & PMOS gate on STI interconnect contact 4542 and the NMOS and PMOSdrain contact 4544 are masked and etched in a second contact step. Thenthe PMOS level contacts are masked and etched: the PMOS gateinterconnect on STI contact 4550, the PMOS only source contact 4552, andthe PMOS only drain contact 4554 in a third contact step. Alternatively,the shallowest contacts may be masked and etched first, followed by themid-level, and then the deepest contacts. The metal lines are maskdefined and etched, filled with barrier metals and copper interconnect,and CMP'ed in a normal Dual Damascene interconnect scheme, therebycompleting the eight types of contact connections.

With reference to the 2D CMOS inverter cell schematic and layoutillustrated in FIG. 42, the above process flow may be used to constructa compact 3D CMOS inverter cell example as illustrated in FIGS. 46A thru46C. The topside view of the 3D cell is illustrated in FIG. 46A wherethe STI (shallow trench isolation) 4600 for both NMOS and PMOS is drawncoincident and the PMOS is on top of the NMOS.

The X direction cross sectional view is illustrated in FIG. 46B and theY direction cross sectional view is illustrated in FIG. 46C. The NMOSand PMOS gates 4602 are drawn coincident and stacked, and are connectedby an NMOS gate on STI to PMOS gate on STI contact 4604, which issimilar to contact 4542 in FIG. 45G. This is the connection for inverterinput signal A as illustrated in FIG. 42. The N+ source contact to theground plane 4606, which is similar to contact 4406 in FIG. 44B, inFIGS. 46A & C makes the NMOS source to ground connection 4206illustrated in FIG. 42. The PMOS source contacts 4608, which are similarto contact 4552 in FIG. 45G, make the PMOS source connection to +V 4207as shown in FIG. 42. The NMOS and PMOS drain shared contacts 4610, whichare similar to contact 4544 in FIG. 45G, make the shared connection 4208as the output Y in FIG. 42. The ground to ground plane contact, similarto contact 4532 in FIG. 45G, is not shown. This contact may not beneeded in every cell and may be shared.

Other 3D logic or memory bit cells may be constructed in a similarfashion. An example of a typical 2D 2-input NOR cell schematic andlayout is illustrated in FIG. 47. The NMOS transistors 4702 and the PMOStransistors 4704 are laid out side by side and are in differently dopedwells. The NMOS sources 4706 are typically grounded, both of the NMOSdrains and one of the PMOS drains 4708 are electrically tied together togenerate the output Y, and the NMOS & PMOS gates 4710 are electricallypaired together for input A or input B. The structure built in 3Ddescribed below will take advantage of these connections in the 3rddimension.

The above process flow may be used to construct a compact 3D 2-input NORcell example as illustrated in FIGS. 48A thru 48C. The topside view ofthe 3D cell is illustrated in FIG. 48A where the STI (shallow trenchisolation) 4800 for both NMOS and PMOS is drawn coincident on the bottomand sides, and not on the top silicon layer to allow NMOS drain onlyconnections to be made. The cell X cross sectional view is illustratedin FIG. 48B and the Y cross sectional view is illustrated in FIG. 48C.

The NMOS and PMOS gates 4802 are drawn coincident and stacked, and eachare connected by a NMOS gate on STI to PMOS gate on STI contact 4804,which is similar to contact 4542 in FIG. 45G. These are the connectionsfor input signals A & B as illustrated in FIG. 47.

The N+ source contact to the ground plane 4806 in FIGS. 48A & C makesthe NMOS source to ground connection 4706 illustrated in FIG. 47. ThePMOS source contacts 4808, which are similar to contact 4552 in FIG.45G, make the PMOS source connection to +V 4707 as shown in FIG. 47. TheNMOS and PMOS drain shared contacts 4810, which are similar to contact4544 in FIG. 45G, make the shared connection 4708 as the output Y inFIG. 47. The NMOS source contacts 4812, which are similar to contact4540 in FIG. 45, make the NMOS connection to Output Y, which isconnected to the NMOS and PMOS drain shared contacts 4810 with metal toform output Y in FIG. 47. The ground to ground plane contact, similar tocontact 4532 in FIG. 45G, is not shown. This contact may not be neededin every cell and may be shared.

The above process flow may be used to construct an alternative compact3D 2-input NOR cell example as illustrated in FIGS. 49A thru 49C. Thetopside view of the 3D cell is illustrated in FIG. 49A where the STI(shallow trench isolation) 4900 for both NMOS and PMOS may be drawncoincident on the top and sides, but not on the bottom silicon layer toallow isolation between the NMOS-A and NMOS-B transistors and allowindependent gate connections. The NMOS or PMOS transistors referred towith the letter-A or -B identify which NMOS or PMOS transistor gate isconnected to, either the A input or the B input, as illustrated in FIG.47. The cell X cross sectional view is illustrated in FIG. 49B and the Ycross sectional view is illustrated in FIG. 49C.

The PMOS-B gate 4902 may be drawn coincident and stacked with dummy gate4904, and the PMOS-B gate 4902 is connected to input B by PMOS gate onlyon STI contact 4908. Both the NMOS-A gate 4910 and NMOS-B gate 4912 aredrawn underneath the PMOS-A gate 4906. The NMOS-A gate 4910 and thePMOS-A gate 4912 are connected together and to input A by NMOS gate onSTI to PMOS gate on STI contact 4914, which is similar to contact 4542in FIG. 45G. The NMOS-B gate 4912 is connected to input B by a NMOS onlygate on STI contact 4916, which is similar to contact 4546 illustratedin FIG. 45G. These are the connections for input signals A & B 4710 asillustrated in FIG. 47.

The N+ source contact to the ground plane 4918 in FIGS. 49A & C formsthe NMOS source to ground connection 4706 illustrated in FIG. 47 and issimilar to ground connection 4406 in FIG. 44B. The PMOS-B sourcecontacts 4920 to Vdd, which are similar to contact 4552 in FIG. 45G,form the PMOS source connection to +V 4707 as shown in FIG. 47. TheNMOS-A, NMOS-B, and PMOS-B drain shared contacts 4922, which are similarto contact 4544 in FIG. 45G, form the shared connection 4708 as theoutput Y in FIG. 47. The ground to ground plane contact, similar tocontact 4532 in FIG. 45G, is not shown. This contact may not be neededin every cell and may be shared.

The above process flow may also be used to construct a CMOS transmissiongate. An example of a typical 2D CMOS transmission gate schematic andlayout is illustrated in FIG. 50A. The NMOS transistor 5002 and the PMOStransistor 5004 are laid out side by side and are in differently dopedwells. The control signal A as the NMOS gate input 5006 and itscomplement Ā as the PMOS gate input 5008 allow a signal from the inputto fully pass to the output when both NMOS and PMOS transistors areturned on (A=1, Ā=0), and not to pass any input signal when both areturned off (A=0, Ā=1). The NMOS and PMOS sources 5010 are electricallytied together and to the input, and the NMOS and PMOS drains 5012 areelectrically tied together to generate the output. The structure builtin 3D described below will take advantage of these connections in the3rd dimension.

The above process flow may be used to construct a compact 3D CMOStransmission cell example as illustrated in FIGS. 50B thru 50D. Thetopside view of the 3D cell is illustrated in FIG. 50B where the STI(shallow trench isolation) 5000 for both NMOS and PMOS may be drawncoincident on the top and sides. The cell X cross sectional view isillustrated in FIG. 50C and the Y cross sectional view is illustrated inFIG. 50D. The PMOS gate 5014 may be drawn coincident and stacked withthe NMOS gate 5016. The PMOS gate 5014 is connected to control signal Ā5008 by PMOS gate only on STI contact 5018. The NMOS gate 5016 isconnected to control signal A 5006 by NMOS gate only on STI contact5020. The NMOS and PMOS source shared contacts 5022 make the sharedconnection 5010 for the input in FIG. 50A. The NMOS and PMOS drainshared contacts 5024 make the shared connection 5012 for the output inFIG. 50A.

Additional logic and memory bit cells, such as a 2-input NAND gate, atransmission gate, an MOS driver, a flip-flop, a 6T SRAM, a floatingbody DRAM, a CAM (Content Addressable Memory) array, etc. may besimilarly constructed with this 3D process flow and methodology.

Another more compact 3D library may be constructed whereby one or morelayers of metal interconnect may be allowed between the NMOS and PMOSdevices. This methodology may allow more compact cell constructionespecially when the cells are complex; however, the top PMOS devicesshould now be made with a low-temperature layer transfer and transistorformation process as shown previously, unless the metals between theNMOS and PMOS layers are constructed with refractory metals, such as,for example, Tungsten.

Accordingly, the library process flow proceeds as described above forFIGS. 43 and 44. Then the layer or layers of conventional metalinterconnect may be constructed on top of the NMOS devices, and thenthat wafer is treated as the acceptor wafer or ‘House’ wafer 808 and thePMOS devices may be layer transferred and constructed in one of the lowtemperature flows as shown in FIGS. 21, 22, 29, 39, and 40.

The above process flow may be used to construct, for example, a compact3D CMOS 6-Transistor SRAM (Static Random Access Memory) cell asillustrated, for example, in FIGS. 51A thru 51D. The SRAM cell schematicis illustrated in FIG. 51A. Access to the cell is controlled by the wordline transistors M5 and M6 where M6 is labeled as 5106. These accesstransistors control the connection to the bit line 5122 and the bit linebar line 5124. The two cross coupled inverters M1-M4 are pulled high toVdd 5108 with M1 or M2 5102, and are pulled to ground 5110 thrutransistors M3 or M4 5104.

The topside NMOS, with no metal shown, view of the 3D SRAM cell isillustrated in FIG. 51B, the SRAM cell X cross sectional view isillustrated in FIG. 51C, and the Y cross sectional view is illustratedin FIG. 51D. NMOS word line access transistor M6 5106 is connected tothe bit line bar 5124 with a contact to NMOS metal 1. The NMOS pull downtransistor 5104 is connected to the ground line 5110 by a contact toNMOS metal 1 and to the back plane N+ ground layer. The bit line 5122 inNMOS metal 1 and transistor isolation oxide 5100 are illustrated. TheVdd supply 5108 is brought into the cell on PMOS metal 1 and connectedto M2 5102 thru a contact to P+. The PMOS poly on STI to NMOS poly onSTI contact 5112 connects the gates of both M2 5102 and M4 5104 toillustrate the 3D cross coupling. The common drain connection of M2 andM4 to the bit bar access transistor M6 is made thru the PMOS P+ to NMOSN+ contact 5114.

The above process flow may also be used to construct a compact 3D CMOS 2Input NAND cell example as illustrated in FIGS. 62A thru 62D. The NAND-2cell schematic and 2D layout is illustrated in FIG. 62A. The two PMOStransistor 6201 sources 6211 are tied together and to V+ supply and thePMOS drains are tied together and to one NMOS drain 6213 and to theoutput Y. Input A 6203 is tied to one PMOS gate and one NMOS gate. InputB 6204 is tied to the other PMOS and NMOS gates. The NMOS A drain istied 6220 to the NMOS B source, and the PMOS B drain 6212 is tied toground. The structure built in 3D described below will take advantage ofthese connections in the 3rd dimension.

The topside view of the 3D NAND-2 cell, with no metal shown, isillustrated in FIG. 62B, the NAND-2 cell X cross sectional views isillustrated in FIG. 62C, and the Y cross sectional view is illustratedin FIG. 62D. The two PMOS sources 6211 are tied together in the PMOSsilicon layer and to the V+ supply metal 6216 in the PMOS metal 1 layerthru a contact. The NMOS A drain and the PMOS A drain are tied 6213together with a thru P+ to N+ contact and to the Output Y metal 6217 inPMOS metal 2, and also connected to the PMOS B drain contact thru PMOSmetal 1 6215. Input A on PMOS metal 2 6214 is tied 6203 to both the PMOSA gate and the NMOS A gate with a PMOS gate on STI to NMOS gate on STIcontact. Input B is tied 6204 to the PMOS B gate and the NMOS B using aP+ gate on STI to NMOS gate on STI contact. The NMOS A source and theNMOS B drain are tied together 6220 in the NMOS silicon layer. The NMOSB source 6212 is tied connected to the ground line 6218 by a contact toNMOS metal 1 and to the back plane N+ ground layer. The transistorisolation oxides 6200 are illustrated.

Another compact 3D library may be constructed whereby one or more layersof metal interconnect is allowed between more than two NMOS and PMOSdevice layers. This methodology allows a more compact cell constructionespecially when the cells are complex; however, devices above the firstNMOS layer should now be made with a low temperature layer transfer andtransistor formation process as shown previously.

Accordingly, the library process flow proceeds as described above forFIGS. 43 and 44. Then the layer or layers of conventional metalinterconnect may be constructed on top of the NMOS devices, and thenthat wafer is treated as the acceptor wafer or house 808 and the PMOSdevices may be layer transferred and constructed in one of the lowtemperature flows as shown in FIGS. 21, 22, 29, 39, and 40. And thenthis low temperature process may be repeated again to form another layerof PMOS or NMOS device, and so on.

The above process flow may also be used to construct a compact 3D CMOSContent Addressable Memory (CAM) array as illustrated in FIGS. 53A to53E. The CAM cell schematic is illustrated in FIG. 53A. Access to theSRAM cell is controlled by the word line transistors M5 and M6 where M6is labeled as 5332. These access transistors control the connection tothe bit line 5342 and the bit line bar line 5340. The two cross coupledinverters M1-M4 are pulled high to Vdd 5334 with M1 or M2 5304, and arepulled to ground 5330 thru transistors M3 or M4 5306. The match line5336 delivers comparison circuit match or mismatch state to the matchaddress encoder. The detect line 5316 and detect line bar 5318 selectthe comparison circuit cell for the address search and connect to thegates of the pull down transistors M8 and M10 5326 to ground 5322. TheSRAM state read transistors M7 and M9 5302 gates are connected to theSRAM cell nodes n1 and n2 to read the SRAM cell state into thecomparison cell. The structure built in 3D described below may takeadvantage of these connections in the 3rd dimension.

The topside top NMOS view of the 3D CAM cell, without metals shown, isillustrated in FIG. 53B, the topside top NMOS view of the 3D CAM cell,with metal shown, is illustrated in FIG. 53C, the 3DCAM cell X crosssectional view is illustrated in FIG. 53D, and the Y cross sectionalview is illustrated in FIG. 53E. The bottom NMOS word line accesstransistor M6 5332 is connected to the bit line bar 5342 with an N+contact to NMOS metal 1. The bottom NMOS pull down transistor 5306 isconnected to the ground line 5330 by an N+ contact to NMOS metal 1 andto the back plane N+ ground layer. The bit line 5340 is in NMOS metal 1and transistor isolation oxides 5300 are illustrated. The ground 5322 isbrought into the cell on top NMOS metal-2. The Vdd supply 5334 isbrought into the cell on PMOS metal-1 5334 and connects to M2 5304 thrua contact to P+. The PMOS poly on STI to bottom NMOS poly on STI contact5314 connects the gates of both M2 5304 and M4 5306 to illustrate theSRAM 3D cross coupling and connects to the comparison cell node n1 thruPMOS metal-1 5312. The common drain connection of M2 and M4 to the bitbar access transistor M6 is made thru the PMOS P+ to NMOS N+ contact5320 and connects node n2 to the M9 gate 5302 via PMOS metal-1 5310 andmetal to gate on STI contact 5308. Top NMOS comparison cell groundpulldown transistor M10 gate 5326 is connected to detect line 5316 witha NMOS metal-2 to gate poly on STI contact. The detect line bar 5318 intop NMOS metal-2 connects thru contact 5324 to the gate of M8 in the topNMOS layer. The match line 5336 in top NMOS metal-2 connects to thedrain side of M9 and M7.

Another compact 3D library may be constructed whereby one or more layersof metal interconnect is allowed between the NMOS and PMOS devices andone or more of the devices is constructed vertically.

A compact 3D CMOS 8 Input NAND cell may be constructed as illustrated inFIGS. 63A thru 63G. The NAND-8 cell schematic and 2D layout isillustrated in FIG. 63A. The eight PMOS transistor 6301 sources 6311 aretied together and to V+ supply and the PMOS drains are tied together6313 and to the NMOS A drain and to the output Y. Inputs A to H are tiedto one PMOS gate and one NMOS gate. Input A is tied to the PMOS A gateand NMOS A gate, input B is tied to the PMOS B gate and NMOS B gate, andso forth through input H is tied to the PMOS H gate and NMOS H gate. Theeight NMOS transistors are coupled in series between the output Y andthe PMOS drains 6313 and ground. The structure built in 3D describedbelow will take advantage of these connections in the 3rd dimension.

The topside view of the 3D NAND-8 cell, with no metal shown and withhorizontal NMOS and PMOS devices, is illustrated in FIG. 63B, the cell Xcross sectional views is illustrated in FIG. 63C, and the Y crosssectional view is illustrated in FIG. 63D. The NAND-8 cell with verticalPMOS and horizontal NMOS devices are shown in FIG. 63E for topside view,63F for the X cross section view, and 63H for the Y cross sectionalview. The same reference numbers are used for analogous structures inthe embodiment shown in FIGS. 63B through 63D and the embodiment shownin FIGS. 63E through 63G. The eight PMOS sources 6311 are tied togetherin the PMOS silicon layer and to the V+ supply metal 6316 in the PMOSmetal 1 layer thru P+ to Metal contacts. The NMOS A drain and the PMOS Adrain are tied 6313 together with a thru P+ to N+ contact 6317 and tothe output Y supply metal 6315 in PMOS metal 2, and also connected tosubstantially all of the PMOS drain contacts thru PMOS metal 1 6315.Input A on PMOS metal 2 6314 is tied 6303 to both the PMOS A gate andthe NMOS A gate with a PMOS gate on STI to NMOS gate on STI contact6314. Substantially all the other inputs are tied to P and N gates insimilar fashion. The NMOS A source and the NMOS B drain are tiedtogether 6320 in the NMOS silicon layer. The NMOS H source 6232 is tiedconnected to the ground line 6318 by a contact to NMOS metal 1 and tothe back plane N+ ground layer. The transistor isolation oxides 6300 areillustrated.

A compact 3D CMOS 8 Input NOR may be constructed as illustrated in FIGS.64A thru 64G. The NOR-8 cell schematic and 2D layout is illustrated inFIG. 64A. The PMOS H transistor source 6411 may be tied to V+ supply.The NMOS drains are tied together 6413 and to the drain of PMOS A and toOutput Y. Inputs A to H are tied to one PMOS gate and one NMOS gate.Input A is tied 6403 to the PMOS A gate and NMOS A gate. The NMOSsources are substantially all tied 6412 to ground. The PMOS H drain istied 6420 to the next PMOS source in the stack, PMOS G, and repeated soforth. The structure built in 3D described below will take advantage ofthese connections in the 3rd dimension.

The topside view of the 3D NOR-8 cell, with no metal shown and withhorizontal NMOS and PMOS devices, is illustrated in FIG. 64B, the cell Xcross sectional views is illustrated in FIG. 64C, and the Y crosssectional view is illustrated in FIG. 64D. The NAND-8 cell with verticalPMOS and horizontal NMOS devices are shown in FIG. 64E for topside view,64F for the X cross section view, and 64G for the Y cross sectionalview. The PMOS H source 6411 is tied to the V+ supply metal 6416 in thePMOS metal 1 layer thru a P+ to Metal contact. The PMOS H drain is tied6420 to PMOS G source in the PMOS silicon layer. The NMOS sources 6412are substantially all tied to ground by N+ to NMOS metal-1 contacts tometal lines 6418 and to the backplane N+ ground layer in the N−substrate. Input A on PMOS metal-2 is tied to both PMOS and NMOS gates6403 with a gate on STI to gate on STI contact 6414. The NMOS drains aresubstantially all tied together with NMOS metal-2 6415 to the NMOS Adrain and PMOS A drain 6413 by the P+ to N+ to PMOS metal-2 contact6417, which is tied to output Y. FIG. 64G illustrates the use ofvertical PMOS transistors to compactly tie the stack sources and drain,and make a very compact area cell shown in FIG. 64E. The transistorisolation oxides 6400 are illustrated.

Accordingly a CMOS circuit may be constructed where the various circuitcells are built on two silicon layers achieving a smaller circuit areaand shorter intra and inter transistor interconnects. As interconnectsbecome dominating for power and speed, packing circuits in a smallerarea would result in a lower power and faster speed end device.

Persons of ordinary skill in the art will appreciate that a number ofdifferent process flows have been described with exemplary logic gatesand memory bit cells used as representative circuits. Such skilledpersons will further appreciate that whichever flow is chosen for anindividual design, a library of all the logic functions for use in thedesign may be created so that the cells may easily be reused eitherwithin that individual design or in subsequent ones employing the sameflow. Such skilled persons will also appreciate that many differentdesign styles may be used for a given design. For example, a library oflogic cells could be built in a manor that has uniform height calledstandard cells as is well known in the art. Alternatively, a librarycould be created for use in long continuous strips of transistors calleda gated array which is also known in the art. In another alternativeembodiment, a library of cells could be created for use in a handcrafted or custom design as is well known in the art. For example, inyet another alternative embodiment, any combination of libraries oflogic cells tailored to these design approaches can be used in aparticular design as a matter of design choice, the libraries chosen mayemploy the same process flow if they are to be used on the same layersof a 3D IC. Different flows may be used on different levels of a 3D IC,and one or more libraries of cells appropriate for each respective levelmay be used in a single design.

Also known in the art are computer program products that may be storedin computer readable media for use in data processing systems employedto automate the design process, more commonly known as computer aideddesign (CAD) software. Persons of ordinary skill in the art willappreciate the advantages of designing the cell libraries in a mannercompatible with the use of CAD software.

Persons of ordinary skill in the art will realize that libraries of I/Ocells, analog function cells, complete memory blocks of various types,and other circuits may also be created for one or more processing flowsto be used in a design and that such libraries may also be madecompatible with CAD software. Many other uses and embodiments willsuggest themselves to such skilled persons after reading thisspecification, thus the scope of the invention is to be limited only bythe appended claims.

Additionally, when circuit cells are built on two or more layers of thinsilicon as shown above, and enjoy the dense vertical thru silicon viainterconnections, the metallization layer scheme to take advantage ofthis dense 3D technology may be improved as follows. FIG. 59 illustratesthe prior art of silicon integrated circuit metallization schemes. Theconventional transistor silicon layer 5902 is connected to the firstmetal layer 5910 thru the contact 5904. The dimensions of thisinterconnect pair of contact and metal lines generally are at theminimum line resolution of the lithography and etch capability for thattechnology process node. Traditionally, this is called a “1×’ designrule metal layer. Usually, the next metal layer is also at the “1×’design rule, the metal line 5912 and via below 5905 and via above 5906that connects metals 5912 with 5910 or with 5914 where desired. Then thenext few layers are often constructed at twice the minimum lithographicand etch capability and called ‘2×’ metal layers, and have thicker metalfor higher current carrying capability. These are illustrated with metalline 5914 paired with via 5907 and metal line 5916 paired with via 5908in FIG. 59. Accordingly, the metal via pairs of 5918 with 5909, and 5920with bond pad opening 5922, represent the ‘4×’ metallization layerswhere the planar and thickness dimensions are again larger and thickerthan the 2× and 1× layers. The precise number of 1× or 2× or 4× layersmay vary depending on interconnection needs and other requirements;however, the general flow is that of increasingly larger metal line,metal space, and via dimensions as the metal layers are farther from thesilicon transistors and closer to the bond pads.

The metallization layer scheme may be improved for 3D circuits asillustrated in FIG. 60. The first mono- or poly-crystalline silicondevice layer 6024 is illustrated as the NMOS silicon transistor layerfrom the above 3D library cells, but may also be a conventional logictransistor silicon substrate or layer. The ‘1×’ metal layers 6020 and6019 are connected with contact 6010 to the silicon transistors and vias6008 and 6009 to each other or metal line 6018. The 2× layer pairs metal6018 with via 6007 and metal 6017 with via 6006. The 4× metal layer 6016is paired with via 6005 and metal 6015, also at 4×. However, now via6004 is constructed in 2× design rules to enable metal line 6014 to beat 2×. Metal line 6013 and via 6003 are also at 2× design rules andthicknesses. Vias 6002 and 6001 are paired with metal lines 6012 and6011 at the 1× minimum design rule dimensions and thickness. The thrusilicon via 6000 of the illustrated PMOS layer transferred silicon 6022may then be constructed at the 1× minimum design rules and provide formaximum density of the top layer. The precise numbers of 1× or 2× or 4×layers may vary depending on circuit area and current carryingmetallization design rules and tradeoffs. The layer transferred toptransistor layer 6022 may be any of the low temperature devicesillustrated herein.

When a transferred layer is not optically transparent to shorterwavelength light, and hence not able to detect alignment marks andimages to a nanometer or tens of nanometer resolution, due to thetransferred layer or its carrier or holder substrate's thickness,infra-red (IR) optics and imaging may be utilized for alignmentpurposes. However, the resolution and alignment capability may not besatisfactory. In some embodiments of the present invention, alignmentwindows are created that allow use of the shorter wavelength light foralignment purposes during layer transfer flows.

As illustrated in FIG. 111A, a generalized process flow may begin with adonor wafer 11100 that is preprocessed with layers 11102 of conducting,semi-conducting or insulating materials that may be formed bydeposition, ion implantation and anneal, oxidation, epitaxial growth,combinations of above, or other semiconductor processing steps andmethods. The donor wafer 11100 may also be preprocessed with a layertransfer demarcation plane 11199, such as, for example, a hydrogenimplant cleave plane, before or after layers 11102 are formed, or may bethinned by other methods previously described. Alignment windows 11130may be lithographically defined, plasma/RIE etched substantially throughlayers 11102, layer transfer demarcation plane 11199, and donor wafer11100, and then filled with shorter wavelength transparent material,such as, for example, silicon dioxide, and planarized with chemicalmechanical polishing (CMP). Optionally, donor wafer 11100 may be furtherthinned by CMP. The size and placement on donor wafer 11100 of thealignment windows 11130 may be determined based on the maximummisalignment tolerance of the alignment scheme used while bonding thedonor wafer 11100 to the acceptor wafer 11110, and the placementlocations of the acceptor wafer alignment marks 11190. Alignment windows11130 may be processed before or after layers 11102 are formed. Acceptorwafer 11110 may be a preprocessed wafer that has fully functionalcircuitry or may be a wafer with previously transferred layers, or maybe a blank carrier or holder wafer, or other kinds of substrates and maybe called a target wafer. The acceptor wafer 11110 and the donor wafer11100 may be, for example, a bulk mono-crystalline silicon wafer or aSilicon On Insulator (SOI) wafer or a Germanium on Insulator (GeOI)wafer. Acceptor wafer 11110 metal connect pads or strips 11180 andacceptor wafer alignment marks 11190 are shown.

Both the donor wafer 11100 and the acceptor wafer 11110 bonding surfaces11101 and 11111 may be prepared for wafer bonding by depositions,polishes, plasma, or wet chemistry treatments to facilitate successfulwafer to wafer bonding.

As illustrated in FIG. 111B, the donor wafer 11100 with layers 11102,alignment windows 11130, and layer transfer demarcation plane 11199 maythen be flipped over, high resolution aligned to acceptor waferalignment marks 11190, and bonded to the acceptor wafer 11110.

As illustrated in FIG. 111C, the donor wafer 11100 may be cleaved at orthinned as described elsewhere in this document to approximately thelayer transfer demarcation plane 11199, leaving a portion of the donorwafer 11100′, alignment windows 11130′ and the pre-processed layers11102 aligned and bonded to the acceptor wafer 11110.

As illustrated in FIG. 111D, the remaining donor wafer portion 11100′may be removed by polishing or etching and the transferred layers 11102may be further processed to create donor wafer device structures 11150that are precisely aligned to the acceptor wafer alignment marks 11190,and the alignment windows 11130′ may be further processed into alignmentwindow regions 11131. These donor wafer device structures 11150 mayutilize thru layer vias (TLVs) 11160 to electrically couple the donorwafer device structures 11150 to the acceptor wafer metal connect padsor strips 11180. As the transferred layers 11102 are thin, on the orderof 200 nm or less in thickness, the TLVs may be easily manufactured as anormal metal to metal via may be, and said TLV may have state of the artdiameters such as nanometers or tens of nanometers. TLV 11160 may bedrawn in the database (not shown) so that it is positioned approximatelyat the center of the acceptor wafer metal connect pads or strips 11180and donor wafer devices structure metal connect pads or strips, and,hence, may be away from the ends of acceptor wafer metal connect pads orstrips 11180 and donor wafer devices structure metal connect pads orstrips at distances greater than approximately the nominal layer tolayer misalignment margin.

Additionally, when monolithically stacking multiple layers oftransistors and circuitry, there may be a practical limit on how manylayers can be effectively stacked. For example, the processing time inthe wafer fabrication facility may be too long or yield too risky for astack of 8 layers, and yet it may be acceptable for creating 4 layerstacks. It therefore may be desirable to create two 4 layer sub-stacks,that may be tested and error or yield corrected with, for example,redundancy schemes described elsewhere in the document, and then stackthe two 4-layer sub-stacks to create the desired 8-layer 3D IC stack.The sub-stack transferred layer and substrate or carrier substrate maynot be optically transparent to shorter wavelength light, and hence notable to detect alignment marks and images to a nanometer or tens ofnanometer resolution, due to the transferred layer or its carrier orholder substrate's thickness or material composition. Infra-red (IR)optics and imaging may be utilized for alignment purposes. However, theresolution and alignment capability may not be satisfactory. In someembodiments of the present invention, alignment windows may be createdthat allow use of the shorter wavelengths of light for alignmentpurposes during layer transfer flows or traditional thru silicon via(TSV) flows as a method to stack and electrically couple the sub-stacks.

As illustrated in FIG. 153A with cross-sectional cuts I and II, ageneralized process flow may begin with a donor wafer 15300 that may bepreprocessed with multiple layers of monolithically stacked transistorsand circuitry sub-stack 15302 by 3D IC methods, including, for example,methods such as described in general in FIG. 8 and in many embodimentsin this document. The donor wafer 15300 may also be preprocessed with alayer transfer demarcation plane 15399, such as, for example, a hydrogenimplant cleave plane, before or after multiple layers of monolithicallystacked transistors and circuitry sub-stack 15302 is formed, or layertransfer demarcation plane 15399 may represent an SOI donor wafer buriedoxide, or may be preprocessed by other methods previously described,such as, for example, use of a heavily boron doped layer. Alignmentwindows 15330 may be lithographically defined and then may be plasma/RIEetched substantially through the multiple layers of monolithicallystacked transistors and circuitry sub-stack 15302, layer transferdemarcation plane 15399, and donor wafer 15300, and may then filled withshorter wavelength transparent material, such as, for example, silicondioxide, and may then be planarized with chemical mechanical polishing(CMP). Optionally, donor wafer 15300 may be further thinned by CMP. Thesize and placement on donor wafer 15300 of the alignment windows 15330may be determined based on the maximum misalignment tolerance of thealignment scheme used while bonding the donor wafer 15300 to theacceptor wafer 15310, and the number and placement locations of theacceptor wafer alignment marks 15390. Alignment windows 15330 may beprocessed before or after each or some of the layers of the multiplelayers of monolithically stacked transistors and circuitry sub-stack15302 are formed.

Acceptor wafer 15310 may be a preprocessed wafer with multiple layers ofmonolithically stacked transistors and circuitry sub-stack 15305.Acceptor wafer 15310 metal connect pads or strips 15380 and acceptorwafer alignment marks 15390 are shown and may be formed in the topdevice layer of the multiple layers of monolithically stackedtransistors and circuitry sub-stack 15305 (shown), or may be formed inany of the other layers of multiple layers of monolithically stackedtransistors and circuitry sub-stack 15305 (not shown), or may be formedin the substrate portion of the acceptor wafer 15310 (not shown).

Both the donor wafer 15300 and the acceptor wafer 15310 bonding surfaces15301 and 15311 respectively may be prepared for wafer bonding bydepositions, polishes, plasma, or wet chemistry treatments to facilitatesuccessful wafer to wafer bonding.

As illustrated in FIG. 153B with cross-sectional cut I, the donor wafer15300 with the multiple layers of monolithically stacked transistors andcircuitry sub-stack 15302, alignment windows 15330, and layer transferdemarcation plane 15399 may then be flipped over, high resolutionaligned to acceptor wafer alignment marks 15390, and bonded to theacceptor wafer 15310 with multiple layers of monolithically stackedtransistors and circuitry sub-stack 15305. Temperature controlled andprofiled wafer bonding chucks may be utilized to compensate for run-outor other across the wafer and wafer section misalignment or expansionoffsets.

As illustrated in FIG. 153C with cross-sectional cut I, the donor wafer15300 may be cleaved at or thinned as described elsewhere in thisdocument to approximately the layer transfer demarcation plane 15399,leaving a portion of the donor wafer 15300′, alignment windows 15330′and the pre-processed layers multiple layers of monolithically stackedtransistors and circuitry sub-stack 15302 aligned and bonded to theacceptor wafer 15310 with multiple layers of monolithically stackedtransistors and circuitry sub-stack 15305.

As illustrated in FIG. 153D with cross-sectional cut I, the remainingdonor wafer portion 15300′ may be removed by polishing or etching andthe transferred multiple layers of monolithically stacked transistorsand circuitry sub-stack 15302 may be further processed to create layerto layer or sub-stack to sub-stack connections utilizing methodsincluding, for example, thru layer vias (TLVs) 15360 and metallization15365 to electrically couple the transferred multiple layers ofmonolithically stacked transistors and circuitry sub-stack 15302 donorwafer device structures 15350 to the acceptor wafer metal connect padsor strips 15380. As the thickness of the transferred multiple layers ofmonolithically stacked transistors and circuitry sub-stack 15302increases, traditional via last TSV (Thru Silicon Via) processing may beutilized to electrically couple the transferred multiple layers ofmonolithically stacked transistors and circuitry sub-stack 15302 donorwafer device structures 15350 to the acceptor wafer metal connect padsor strips 15380. TLV 15360 may be drawn in the database (not shown) sothat it is positioned approximately at the center of the acceptor wafermetal connect pads or strips 15380 and donor wafer devices structuremetal connect pads or strips, and, hence, may be away from the ends ofacceptor wafer metal connect pads or strips 15380 and donor waferdevices structure metal connect pads or strips at distances greater thanapproximately the nominal layer to layer misalignment margin.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 153A through 153D are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the acceptor wafer 15310may have alignment windows over the alignment marks formed prior to thealignment and bonding step to the donor wafer. Additionally, a via firstTSV process may be utilized on the donor wafer 15300 prior to the waferto wafer bonding. Moreover, the acceptor wafer 15310 and the donor wafer15300 may be, for example, a bulk mono-crystalline silicon wafer or aSilicon On Insulator (SOI) wafer or a Germanium on Insulator (GeOI)wafer. Further, the opening size of the alignment windows 15330 formedmay be minimized by use of pre-alignment with IR or other longwavelength light, and final high resolution alignment performed thru thealignment windows 15330 with lower wavelength light. Many othermodifications within the scope of the invention will suggest themselvesto such skilled persons after reading this specification. Thus theinvention is to be limited only by the appended claims.

As illustrated in FIG. 154A with cross-sectional cuts I and II, ageneralized process flow utilizing a carrier wafer or substrate maybegin with a donor wafer 15400 that may be preprocessed with multiplelayers of monolithically stacked transistors and circuitry sub-stack15402 by 3D IC methods, including, for example, methods such asdescribed in general in FIG. 8 and in many embodiments in this document.The donor wafer 15400 may also be preprocessed with a layer transferdemarcation plane 15499, such as, for example, a hydrogen implant cleaveplane, before or after multiple layers of monolithically stackedtransistors and circuitry sub-stack 15402 is formed, or layer transferdemarcation plane 15499 may represent an SOI donor wafer buried oxide,or may be preprocessed by other methods previously described, such as,for example, use of a heavily boron doped layer. Alignment windows 15430may be lithographically defined and may then be plasma/RIE etchedsubstantially through the multiple layers of monolithically stackedtransistors and circuitry sub-stack 15402 and then may be etched toapproximately the layer transfer demarcation plane 15499. In FIG. 154A,the alignment windows 15430 are shown etched past the layer transferdemarcation plane 15499, but may be etched shallower than the layertransfer demarcation plane 15499. The alignment windows 15430 may thenbe filled with shorter wavelength transparent material, such as, forexample, silicon dioxide, and then may be planarized with chemicalmechanical polishing (CMP). The size and placement on donor wafer 15400of the alignment windows 15430 may be determined based on the maximummisalignment tolerance of the alignment scheme used while bonding thedonor wafer 15400 to the acceptor wafer 15410, and the number andplacement locations of the acceptor wafer alignment marks 15490.Alignment windows 15430 may be processed before or after each or some ofthe layers of the multiple layers of monolithically stacked transistorsand circuitry sub-stack 15402 are formed.

Acceptor wafer 15410 may be a preprocessed wafer with multiple layers ofmonolithically stacked transistors and circuitry sub-stack 15405.Acceptor wafer 15410 metal connect pads or strips 15480 and acceptorwafer alignment marks 15490 are shown and may be formed in the topdevice layer of the multiple layers of monolithically stackedtransistors and circuitry sub-stack 15405 (shown), or may be formed inany of the other layers of multiple layers of monolithically stackedtransistors and circuitry sub-stack 15405 (not shown), or may be formedin the substrate portion of the acceptor wafer 15410 (not shown).

As illustrated in FIG. 154B with cross-sectional cut I, carriersubstrate 15480, such as, for example, a glass or quartz substrate, maybe temporarily bonded to the donor wafer at surface 15401. Some carriersubstrate temporary bonding methods and materials are describedelsewhere in this document.

As illustrated in FIG. 154C with cross-sectional cut I, the donor wafer15400 may be substantially thinned by previously described processes,such as, for example, cleaving at the layer transfer demarcation plane15499 and polishing with CMP to approximately the bottom of the STIstructures. The STI structures are in the bottom layer of the donorwafer sub-stack multiple layers of monolithically stacked transistorsand circuitry sub-stack 15402. Alignment windows 15481 are thus formed.

Both the carrier substrate 15480 with donor wafer sub-stack multiplelayers of monolithically stacked transistors and circuitry sub-stack15402 and the acceptor wafer 15410 bonding surfaces 15481 and 15411respectively may be prepared for wafer bonding by depositions, polishes,plasma, or wet chemistry treatments to facilitate successful wafer towafer bonding.

As illustrated in FIG. 154D with cross-sectional cut I, the carriersubstrate 15480 with donor wafer multiple layers of monolithicallystacked transistors and circuitry sub-stack 15402 and alignment windows15431, may then be high resolution aligned to acceptor wafer alignmentmarks 15490, and may be bonded to the acceptor wafer 15410 with multiplelayers of monolithically stacked transistors and circuitry sub-stack15405 at acceptor bonding surface 15411 and donor wafer bonding surface15481. Temperature controlled and profiled wafer bonding chucks may beutilized to compensate for run-out or other across the wafer and wafersection misalignment or expansion offsets.

As illustrated in FIG. 154E with cross-sectional cut I, the carriersubstrate 15480 may be detached with processes described elsewhere inthis document, for example, with laser ablation of a polymeric adhesionlayer, thus leaving alignment windows 15431 and the pre-processedmultiple layers of monolithically stacked transistors and circuitrysub-stack 15402 aligned and bonded to the acceptor wafer 15410 withmultiple layers of monolithically stacked transistors and circuitrysub-stack 15405, acceptor wafer 15410 metal connect pads or strips15480, and acceptor wafer alignment marks 15490.

As illustrated in FIG. 154F with cross-sectional cut I, the transferredmultiple layers of monolithically stacked transistors and circuitrysub-stack 15402 may be further processed to create layer to layer orsub-stack to sub-stack connections utilizing methods including, forexample, thru layer vias (TLVs) 15460 and metallization 15465 toelectrically couple the transferred multiple layers of monolithicallystacked transistors and circuitry sub-stack 15402 donor wafer devicestructures 15450 to the acceptor wafer metal connect pads or strips15480. As the thickness of the transferred multiple layers ofmonolithically stacked transistors and circuitry sub-stack 15402increases, traditional via last TSV (Thru Silicon Via) processing may beutilized to electrically couple the transferred multiple layers ofmonolithically stacked transistors and circuitry sub-stack 15402 donorwafer device structures 15450 to the acceptor wafer metal connect padsor strips 15480. TLV 15460 may be drawn in the database (not shown) sothat it is positioned approximately at the center of the acceptor wafermetal connect pads or strips 15480 and donor wafer devices structuremetal connect pads or strips, and, hence, may be away from the ends ofacceptor wafer metal connect pads or strips 15480 and donor waferdevices structure metal connect pads or strips at distances greater thanapproximately the nominal layer to layer misalignment margin.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 154A through 154F are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the acceptor wafer 15410may have alignment windows over the alignment marks formed prior to thealignment and bonding step to the donor wafer. Additionally, a via firstTSV process may be utilized on the donor wafer 15400 prior to the waferto wafer bonding. Moreover, the acceptor wafer 15410 and the donor wafer15400 may be, for example, a bulk mono-crystalline silicon wafer or aSilicon On Insulator (SOI) wafer or a Germanium on Insulator (GeOI)wafer. Further, the carrier substrate may be a silicon wafer with alayer transfer demarcation plane and utilize methods, such aspermanently oxide to oxide bonding the carrier wafer to the donor waferand then cleaving and thinning after bonding to the acceptor wafer,described elsewhere in this document to layer transfer the donor waferdevice layers or sub-stack, to the acceptor wafer. Moreover, the openingsize of the alignment windows 15430 formed may be minimized by use ofpre-alignment with IR or other long wavelength light, and final highresolution alignment performed thru the alignment windows 15430 withlower wavelength light. Many other modifications within the scope of theinvention will suggest themselves to such skilled persons after readingthis specification. Thus the invention is to be limited only by theappended claims.

FIG. 149 describes an embodiment of this present invention, wherein amemory array 14902 may be constructed on a piece of silicon andperipheral transistors 14904 are stacked atop the memory array 14902.The peripheral transistors 14904 may be constructed well-aligned withthe underlying memory array 14902 using any of the schemes described inthis document. For example, the peripheral transistors may bejunction-less transistors, recessed channel transistors or they could beformed with one of the repeating layout schemes described in thisdocument. Through-silicon connections 14906 may connect the memory array14902 to the peripheral transistors 14904. The memory array may be DRAMmemory, SRAM memory, flash memory, some type of resistive memory or ingeneral, could be any memory type that is commercially available.

An additional use for the high density of TLVs 11160 in FIG. 111D, orany such TLVs in this document, may be to thermally conduct heatgenerated by the active circuitry from one layer to another connected bythe TLVs, such as, for example, donor layers and device structures toacceptor wafer or substrate. TLVs 11160 may also be utilized to conductheat to an on chip thermoelectric cooler, heat sink, or other heatremoving device. A portion of TLVs on a 3D IC may be utilized primarilyfor electrical coupling, and a portion may be primarily utilized forthermal conduction. In many cases, the TLVs may provide utility for bothelectrical coupling and thermal conduction.

As layers are stacked in a 3D IC, the power density per unit areaincreases. The thermal conductivity of mono-crystalline silicon is poorat 150 W/m-K and silicon dioxide, the most common electrical insulatorin modern silicon integrated circuits, has a very poor thermalconductivity at 1.4 W/m-K. If a heat sink is placed at the top of a 3DIC stack, then the bottom chip or layer (farthest from the heat sink)has the poorest thermal conductivity to that heat sink, since the heatfrom that bottom layer must travel thru the silicon dioxide and siliconof the chip(s) or layer(s) above it.

As illustrated in FIG. 112A, a heat spreader layer 11205 may bedeposited on top of a thin silicon dioxide layer 11203 which isdeposited on the top surface of the interconnect metallization layers11201 of substrate 11202. Heat spreader layer 11205 may include PlasmaEnhanced Chemical Vapor Deposited Diamond Like Carbon (PECVD DLC), whichhas a thermal conductivity of approximately 1000 W/m-K, or anotherthermally conductive material, such as Chemical Vapor Deposited (CVD)graphene (approximately 5000 W/m-K) or copper (approximately 400 W/m-K).Heat spreader layer 5015 may be of thickness approximately 20 nm up toapproximately 1 micron. The preferred thickness range is approximately50 nm to 100 nm and the preferred electrical conductivity of the heatspreader layer 11205 is an insulator to enable minimum design rulediameters of the future thru layer vias. If the heat spreader iselectrically conducting, the TLV openings need to be somewhat enlargedto allow for the deposition of a non-conducting coating layer on the TLVwalls before the conducting core of the TLV is deposited. Alternatively,if the heat spreader layer 11205 is electrically conducting, it may bemasked and etched to provide the landing pads for the thru layer viasand a large grid around them for heat transfer, which could also be usedas the ground plane or as power and ground straps for the circuits aboveand below it. Oxide layer 11204 may be deposited (and may be planarizedto fill any gaps in the heat transfer layer) to prepare for wafer towafer oxide bonding. Acceptor substrate 11214 may include substrate11202, interconnect metallization layers 11201, thin silicon dioxidelayer 11203, heat spreader layer 11205, and oxide layer 11204. The donorwafer substrate 11206 may be processed with wafer sized layers of dopingas previously described, in preparation for forming transistors andcircuitry (such as, for example, junction-less, RCAT, V-groove, andbipolar) after the layer transfer. A screen oxide 11207 may be grown ordeposited prior to the implant or implants to protect the silicon fromimplant contamination, if implantation is utilized, and to provide anoxide surface for later wafer to wafer bonding. A layer transferdemarcation plane 11299 (shown as a dashed line) may be formed in donorwafer substrate 11206 by hydrogen implantation, ‘ion-cut’ method, orother methods as previously described. Donor wafer 11212 may includedonor substrate 11206, layer transfer demarcation plane 11299, screenoxide 11207, and any other layers (not shown) in preparation for formingtransistors as discussed previously. Both the donor wafer 11212 andacceptor wafer 11214 may be prepared for wafer bonding as previouslydescribed and then bonded at the surfaces of oxide layer 11204 and oxidelayer 11207, at a low temperature (less than approximately 400° C.). Theportion of donor substrate 11206 that is above the layer transferdemarcation plane 11299 may be removed by cleaving and polishing, orother processes as previously described, such as ion-cut or othermethods, thus forming the remaining transferred layers 11206′.Alternatively, donor wafer 11212 may be constructed and then layertransferred, using methods described previously such as, for example,ion-cut with replacement gates (not shown), to the acceptor substrate11214. Now transistors or portions of transistors may be formed andaligned to the acceptor wafer alignment marks (not shown) and thru layervias formed as previously described. Thus, a 3D IC with an integratedheat spreader is constructed.

As illustrated in FIG. 113A, a set of power and ground grids, such asbottom transistor layer power and ground grid 11307 and top transistorlayer power and ground grid 11306, may be connected by thru layer powerand ground vias 11304 and thermally coupled to the electricallynon-conducting heat spreader layer 11305. If the heat spreader is anelectrical conductor, then it could either only be used as a groundplane, or a pattern should be created with power and ground strips inbetween the landing pads for the TLVs. The density of the power andground grids and the thru layer vias to the power and ground grids maybe designed to substantially improve a certain overall thermalresistance for substantially all the circuits in the 3D IC stack.Bonding oxides 11310, printed wiring board 11300, package heat spreader11325, bottom transistor layer 11302, top transistor layer 11312, andheat sink 11330 are shown. Thus, a 3D IC with an integrated heat sink,heat spreaders, and thru layer vias to the power and ground grid isconstructed.

As illustrated in FIG. 113B, thermally conducting material, such asPECVD DLC, may be formed on the sidewalls of the 3D IC structure of FIG.113A to form sidewall thermal conductors 11360 for sideways heatremoval. Bottom transistor layer power and ground grid 11307, toptransistor layer power and ground grid 11306, thru layer power andground vias 11304, heat spreader layer 11305, bonding oxides 11310,printed wiring board 11300, package heat spreader 11325, bottomtransistor layer 11302, top transistor layer 11312, and heat sink 11330are shown.

FIG. 138A illustrates a packaging scheme used for severalhigh-performance microchips. A silicon chip 13802 is attached to anorganic substrate 13804 using solder bumps 13808. The organic substrate13804, in turn, is connected to an FR4 printed wiring board (also calledboard) 13806 using solder bumps 13812. The co-efficient of thermalexpansion (CTE) of silicon is 3.2 ppm/K, the CTE of organic substratesis typically ˜17 ppm/K and the CTE of FR4 material is typically ˜17ppm/K. Due to this large mismatch between CTE of the silicon chip 13802and the organic substrate 13804, the solder bumps 13808 are subjected tostresses, which can cause defects and cracking in solder bumps 13808. Toavoid this potential cause of defects and cracking, underfill material13810 is dispensed between solder bumps. While underfill material 13810can prevent defects and cracking, it can cause other challenges.Firstly, when solder bump sizes are reduced or when high density ofsolder bumps is required, dispensing underfill material becomesdifficult or even impossible, since underfill cannot flow in smallspaces. Secondly, underfill is hard to remove once dispensed. As aresult, if a chip on a substrate is found to have defects, removing thechip and replacing with another chip are difficult. Hence, production ofmulti-chip substrates is difficult. Thirdly, underfill can cause thestress, due to the mismatch of CTE between the silicon chip 13802 andthe substrate 13804, to be more efficiently communicated to the low kdielectric layers present between on-chip interconnects.

FIG. 139B illustrates a packaging scheme used for many low-powermicrochips. A silicon chip 13814 is directly connected to an FR4substrate 13816 using solder bumps 13818. Due to the large difference inCTE between the silicon chip 13814 and the FR4 substrate 13816,underfill 13820 is dispensed many times between solder bumps. Asmentioned previously, underfill brings with it challenges related todifficulty of removal and stress communicated to the chip low kdielectric layers.

In both of the packaging types described in FIG. 139A and FIG. 139B andalso many other packaging methods available in the literature, themismatch of co-efficient of thermal expansion (CTE) between a siliconchip and a substrate, or between a silicon chip and a printed wiringboard, is a serious issue in the packaging industry. A technique tosolve this problem without the use of underfill is advantageous.

FIG. 139A-F describes an embodiment of this present invention, where useof underfill may be avoided in the packaging process of a chipconstructed on a silicon-on-insulator (SOI) wafer. Although thisembodiment of the present invention is described with respect to onetype of packaging scheme, it will be clear to one skilled in the artthat the invention may be applied to other types of packaging. Theprocess flow for the SOI chip could include the following steps thatoccur in sequence from Step (A) to Step (F). When the same referencenumbers are used in different drawing figures (among FIG. 139A-F), theyare used to indicate analogous, similar or identical structures toenhance the understanding of the present invention by clarifying therelationships between the structures and embodiments presented in thevarious diagrams—particularly in relating analogous, similar oridentical functionality to different physical structures.

Step (A) is illustrated in FIG. 139A. An SOI wafer with transistorsconstructed on silicon layer 13906 has a buried oxide 13904 atop siliconregion 13902. Interconnect layers 13908, which may include metals suchas aluminum or copper and insulators such as silicon oxide or low kdielectrics, are constructed as well.Step (B) is illustrated in FIG. 139B. A temporary carrier wafer 13912can be attached to the structure shown in FIG. 139A using a temporarybonding adhesive 13910. The temporary carrier wafer 13912 may beconstructed with a material, such as, for example, glass or silicon. Thetemporary bonding adhesive 13910 may include, for example, a polyimide.Step (C) is illustrated in FIG. 139C. The structure shown in FIG. 139Bmay be subjected to a selective etch process, such as, for example, aPotassium Hydroxide etch, (potentially combined with a back-grindingprocess) where silicon layer 13902 is removed using the buried oxidelayer 13904 as an etch stop. Once the buried oxide layer 13904 isreached during the etch step, the etch process is stopped. The etchchemistry is selected such that it etches silicon but does not etch theburied oxide layer 13904 appreciably. The buried oxide layer 13904 maybe polished with CMP to ensure a planar and smooth surface.Step (D) is illustrated in FIG. 139D. The structure shown in FIG. 139Cmay be bonded to an oxide-coated carrier wafer having a co-efficient ofthermal expansion (CTE) similar to that of the organic substrate usedfor packaging. This oxide-coated carrier wafer as described will becalled a CTE matched carrier wafer henceforth in this document. Thebonding step may be conducted using oxide-to-oxide bonding of buriedoxide layer 13904 to the oxide coating 13916 of the CTE matched carrierwafer 13914. The CTE matched carrier wafer 13914 may include materials,such as, for example, copper, aluminum, organic materials, copper alloysand other materials.Step (E) is illustrated in FIG. 139E. The temporary carrier wafer 13912may be detached from the structure at the surface of the interconnectlayers 13908 by removing the temporary bonding adhesive 13910. Thisdetachment may be done, for example, by shining laser light through theglass temporary carrier wafer 13912 to ablate or heat the temporarybonding adhesive 13910.Step (F) is illustrated in FIG. 139F. Solder bumps 13918 may beconstructed for the structure shown in FIG. 139E. After dicing, thisstructure may be attached to organic substrate 13920. This organicsubstrate may then be attached to a printed wiring board 13924, such as,for example, an FR4 substrate, using solder bumps 13922.

The conditions for choosing the CTE matched carrier wafer 13914 for thisembodiment of the present invention include the following. Firstly, theCTE matched carrier wafer 13914 should have a CTE close to that of theorganic substrate 13920. For example, the CTE of the CTE matched carrierwafer 13914 should be within approximately 10 ppm/K of the CTE of theorganic substrate 13920. Secondly, the volume of the CTE matched carrierwafer 13914 should be much higher than the silicon region 13906. Forexample, the volume of the CTE matched carrier wafer 13914 may begreater than approximately 5 times the volume of the silicon region13906. When this happens, the CTE of the combination of the siliconregion 13906 and the CTE matched carrier 13914 may be close to that ofthe CTE matched carrier 13914. If these two conditions are met, theissues of co-efficient of thermal expansion mismatch describedpreviously are ameliorated, and a reliable packaging process may beobtained without underfill being used.

The organic substrate 13920 typically has a CTE of approximately 17ppm/K and the printed wiring board 13924 typically is constructed of FR4which has a CTE of approximately 18 ppm/K. If the CTE matched carrierwafer is constructed of an organic material having a CTE ofapproximately 17 ppm/K, it can be observed that issues of co-efficientof thermal expansion mismatch described previously are ameliorated, anda reliable packaging process may be obtained without underfill beingused. If the CTE matched carrier wafer is constructed of a copper alloyhaving a CTE of approximately 17 ppm/K, it can be observed that issuesof co-efficient of thermal expansion mismatch described previously areameliorated, and a reliable packaging process may be obtained withoutunderfill being used. If the CTE matched carrier wafer is constructed ofan aluminum alloy material having a CTE of approximately 24 ppm/K, itcan be observed that issues of co-efficient of thermal expansionmismatch described previously are ameliorated, and a reliable packagingprocess may be obtained without underfill being used.

FIG. 140A-F describes an embodiment of this present invention, where useof underfill may be avoided in the packaging process of a chipconstructed on a bulk-silicon wafer. Although this embodiment of thepresent invention is described with respect to one type of packagingscheme, it will be clear to one skilled in the art that the inventionmay be applied to other types of packaging. The process flow for thesilicon chip could include the following steps that occur in sequencefrom Step (A) to Step (F). When the same reference numbers are used indifferent drawing figures (among FIG. 140A-F), they are used to indicateanalogous, similar or identical structures to enhance the understandingof the present invention by clarifying the relationships between thestructures and embodiments presented in the variousdiagrams—particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A) is illustrated in FIG. 140A. A bulk-silicon wafer withtransistors constructed on a silicon layer 14006 may have a buried p+silicon layer 14004 atop silicon region 14002. Interconnect layers14008, which may include metals such as aluminum or copper andinsulators such as silicon oxide or low k dielectrics, may beconstructed. The buried p+silicon layer 14004 may be constructed with aprocess, such as, for example, an ion-implantation and thermal anneal,or an epitaxial doped silicon deposition.Step (B) is illustrated in FIG. 140B. A temporary carrier wafer 14012may be attached to the structure shown in FIG. 140A using a temporarybonding adhesive 14010. The temporary carrier wafer 14012 may beconstructed with a material, such as, for example, glass or silicon. Thetemporary bonding adhesive 14010 may include, for example, a polyimide.Step (C) is illustrated in FIG. 140C. The structure shown in FIG. 140Bmay be subjected to a selective etch process, such as, for example,ethylenediamine pyrocatechol (EDP) (potentially combined with aback-grinding process) where silicon layer 14002 is removed using theburied p+ silicon layer 14004 as an etch stop. Once the buried p+silicon layer 14004 is reached during the etch step, the etch process isstopped. The etch chemistry is selected such that the etch process stopsat the p+ silicon buried layer. The buried p+ silicon layer 14004 maythen be polished away with CMP and planarized. Following this, an oxidelayer 14098 may be deposited.Step (D) is illustrated in FIG. 140D. The structure shown in FIG. 140Cmay be bonded to an oxide-coated carrier wafer having a co-efficient ofthermal expansion (CTE) similar to that of the organic substrate usedfor packaging. The oxide-coated carrier wafer as described will becalled a CTE matched carrier wafer henceforth in this document. Thebonding step may be conducted using oxide-to-oxide bonding of oxidelayer 14098 to the oxide coating 14016 of the CTE matched carrier wafer14014. The CTE matched carrier wafer 14014 may include materials, suchas, for example, copper, aluminum, organic materials, copper alloys andother materials.Step (E) is illustrated in FIG. 140E. The temporary carrier wafer 14012may be detached from the structure at the surface of the interconnectlayers 14008 by removing the temporary bonding adhesive 14010. Thisdetachment may be done, for example, by shining laser light through theglass temporary carrier wafer 14012 to ablate or heat the temporarybonding adhesive 14010.Step (F) is illustrated using FIG. 140F. Solder bumps 14018 may beconstructed for the structure shown in FIG. 140E. After dicing, thisstructure may be attached to organic substrate 14020. This organicsubstrate may then be attached to a printed wiring board 14024, such as,for example, an FR4 substrate, using solder bumps 14022.

There are two key conditions while choosing the CTE matched carrierwafer 14014 for this embodiment of the present invention. Firstly, theCTE matched carrier wafer 14014 should have a CTE close to that of theorganic substrate 14020. Preferably, the CTE of the CTE matched carrierwafer 14014 should be within approximately 10 ppm/K of the CTE of theorganic substrate 14020. Secondly, the volume of the CTE matched carrierwafer 14014 should be much higher than the silicon region 14006.Preferably, the volume of the CTE matched carrier wafer 14014 may be,for example, greater than approximately 5 times the volume of thesilicon region 14006. When this happens, the CTE of the combination ofthe silicon region 14006 and the CTE matched carrier 14014 may be closeto that of the CTE matched carrier 14014. If these two conditions aremet, the issues of co-efficient of thermal expansion mismatch describedpreviously are ameliorated, and a reliable packaging process may beobtained without underfill being used.

The organic substrate 14020 typically has a CTE of approximately 17ppm/K and the printed wiring board 14024 typically is constructed of FR4which has a CTE of approximately 18 ppm/K. If the CTE matched carrierwafer is constructed of an organic material having a CTE of 17 ppm/K, itcan be observed that issues of co-efficient of thermal expansionmismatch described previously are ameliorated, and a reliable packagingprocess may be obtained without underfill being used. If the CTE matchedcarrier wafer is constructed of a copper alloy having a CTE ofapproximately 17 ppm/K, it can be observed that issues of co-efficientof thermal expansion mismatch described previously are ameliorated, anda reliable packaging process may be obtained without underfill beingused. If the CTE matched carrier wafer is constructed of an aluminumalloy material having a CTE of approximately 24 ppm/K, it can beobserved that issues of co-efficient of thermal expansion mismatchdescribed previously are ameliorated, and a reliable packaging processmay be obtained without underfill being used.

While FIG. 139A-F and FIG. 140A-F describe methods of obtaining thinnedwafers using buried oxide and buried p+ silicon etch stop layersrespectively, it will be clear to one skilled in the art that othermethods of obtaining thinned wafers exist. Hydrogen may be implantedthrough the back-side of a bulk-silicon wafer (attached to a temporarycarrier wafer) at a certain depth and the wafer may be cleaved using amechanical force. Alternatively, a thermal or optical anneal may be usedfor the cleave process. An ion-cut process through the back side of abulk-silicon wafer could therefore be used to thin a wafer accurately,following which a CTE matched carrier wafer may be bonded to theoriginal wafer.

It will be clear to one skilled in the art that other methods to thin awafer and attach a CTE matched carrier wafer exist. Other methods tothin a wafer include, but not limited to, CMP, plasma etch, wet chemicaletch, or a combination of these processes. These processes may besupplemented with various metrology schemes to monitor wafer thicknessduring thinning. Carefully timed thinning processes may also be used.

FIG. 141 describes an embodiment of this present invention, wheremultiple dice, such as, for example, dice 14124 and 14126 are placed andattached atop packaging substrate 14116. Packaging substrate 14116 mayinclude packaging substrate high density wiring layers 14114, packagingsubstrate vias 14120, packaging substrate-to-printed-wiring-boardconnections 14118, and printed wiring board 14122. Die-to-substrateconnections 14112 may be utilized to electrically couple dice 14124 and14126 to the packaging substrate high density wiring levels 14114 ofpackaging substrate 14116. The dice 14124 and 14126 may be constructedusing techniques described with FIG. 139A-F and FIG. 140A-F but areattached to packaging substrate 14116 rather than organic substrate13922 or 14022. Due to the techniques of construction described in FIG.139A-F and FIG. 140A-F being used, a high density of connections may beobtained from each die, such as 14124 and 14126, to the packagingsubstrate 14116. By using a packaging substrate 14116 with packagingsubstrate high density wiring levels 14114, a large density ofconnections between multiple dice 14124 and 14126 may be realized. Thisopens up several opportunities for system design. In one embodiment ofthis present invention, unique circuit blocks may be placed on differentdice assembled on the packaging substrate 14116. In another embodiment,contents of a large die may be split among many smaller dice to reduceyield issues. In yet another embodiment, analog and digital blocks couldbe placed on separate dice. It will be obvious to one skilled in the artthat several variations of these concepts are possible. The key enablerfor all these ideas is the fact that the CTEs of the dice are similar tothe CTE of the packaging substrate, so that a high density ofconnections from the die to the packaging substrate may be obtained, andprovide for a high density of connection between dice. 14102 denotes aCTE matched carrier wafer, 14104 and 14106 are oxide layers, 14108represents transistor regions, 14110 represents a multilevel wiringstack, 14112 represents die-to-substrate connections, 14116 representsthe packaging substrate, 14114 represents the packaging substrate highdensity wiring levels, 14120 represents vias on the packaging substrate,14118 denotes packaging substrate-to-printed-wiring-board connectionsand 14122 denotes a printed wiring board.

As well, the independent formation of each transistor layer enables theuse of materials other than silicon to construct transistors. Forexample, a thin III-V compound quantum well channel such as InGaAs andInSb may be utilized on one or more of the 3D layers described above bydirect layer transfer or deposition and the use of buffer compounds suchas GaAs and InAlAs to buffer the silicon and III-V lattice mismatches.This enables high mobility transistors that can be optimizedindependently for p and n-channel use, solving the integrationdifficulties of incorporating n and p III-V transistors on the samesubstrate, and also the difficulty of integrating the III-V transistorswith conventional silicon transistors on the same substrate. Forexample, the first layer silicon transistors and metallization generallycannot be exposed to temperatures higher than 400° C. The III-Vcompounds, buffer layers, and dopings generally need processingtemperatures above that 400° C. threshold. By use of the pre deposited,doped, and annealed layer donor wafer formation and subsequent donor toacceptor wafer transfer techniques described above and illustrated inFIGS. 14, 20 to 29, and 43 to 45, III-V transistors and circuits may beconstructed on top of silicon transistors and circuits without damagingsaid underlying silicon transistors and circuits. As well, any stressmismatches between the dissimilar materials to be integrated, such assilicon and III-V compounds, may be mitigated by the oxide layers, orspecialized buffer layers, that are vertically in-between the dissimilarmaterial layers. Additionally, this now enables the integration ofoptoelectronic elements, communication, and data path processing withconventional silicon logic and memory transistors and silicon circuits.Another example of a material other than silicon that the independentformation of each transistor layer enables is Germanium.

It should be noted that this 3D IC technology could be used for manyapplications. As an example the various structures presented in FIGS. 15to 19 having been constructed in the ‘foundation,’ which may be belowthe main or primary or house layer, could be just as well be‘fabricated’ in the “Attic,” which may be above the main or primary orhouse layer, by using the techniques described in relation to FIGS. 21to 35.

It also should be noted that the 3D programmable system, where the logicfabric is sized by dicing a wafer of tiled array as illustrated in FIG.36, could utilize the ‘monolithic’ 3D techniques related to FIG. 14 inrespect to the ‘Foundation’, or to FIGS. 21 through 35 in respect to theAttic, to add IO or memories as presented in FIG. 11. So while in manycases constructing a 3D programmable system using TSV could bepreferable there might be cases where it will be better to use the‘Foundation’ or ‘Attic”.

When a substrate wafer, carrier wafer, or donor wafer is thinned by acleaving method and a chemical mechanical polish (CMP) in this document,there are other methods that may be employed to thin the wafer. Forexample, a boron implant and anneal may be utilized to create a layer inthe silicon substrate to be thinned that will provide a wet chemicaletch stop plane. A dry etch, such as a halogen gas cluster beam, may beemployed to thin a silicon substrate and then smooth the silicon surfacewith an oxygen gas cluster beam. Additionally, these thinning techniquesmay be utilized independently or in combination to achieve the properthickness and defect free surface as may be needed by the process flow.

FIG. 142A shows the surface of a wafer or substrate structure after alayer transfer and after a hydrogen, or other atomic species, implantplane has been cleaved. The wafer may include a bottom layer oftransistors and wires 14202 with an oxide layer 14204 atop. These inturn have been bonded using oxide-to-oxide bonding and cleaved to astructure such that a silicon dioxide layer 14206, p− Silicon layer14208 and n+ Silicon layer 14210 are formed atop the bottom layer oftransistors and wires 14202 and the oxide layer 14204. The surface ofthe wafer or substrate structure shown in FIG. 142A can often benon-planar after cleaving along a hydrogen plane, with irregularfeatures 14212 formed atop it.

The irregular features 14212 may be removed using a chemical mechanicalpolish (CMP) that planarizes the surface of the wafer or substratestructure.

Alternatively, a process shown in FIG. 142B-C may be utilized to removeor reduce the extent of irregular features 14212 of FIG. 142A. Variouselements in FIG. 142B such as 14202, 14204, 14206 and 14208 are asdescribed in the description for FIG. 142A. The surface of n+ Siliconlayer 14210 and the irregular features 14212 may be subjected to aradical oxidation process that produces thermal oxide layer 14214 atless than 400° C. by using a plasma. The thermal oxide layer 14214consumes a portion of the n+ Silicon region 14210 shown in FIG. 142A toproduce the n+ Si region 14298 of FIG. 142B. The thermal oxide layer14214 may then be etched away, utilizing an etchant such as, forexample, a dilute Hydrofluoric acid solution, to form the structureshown in FIG. 142C. Various elements in FIG. 142C such as 14202, 14204,14206, 14208 and 14298 are as described with respect to FIG. 142B. Itcan be observed that the extent of non-planarities 14216 in FIG. 142C isless than in FIG. 142A. The radical oxidation and etch-back processsmoothens the surface and reduces non-planarities.

Alternatively, according to an embodiment of this present invention,surface non-planarities may be removed or reduced by treating thecleaved surface of the wafer or substrate in a hydrogen plasma at lessthan approximately 400° C. The hydrogen plasma source gases may include,for example, hydrogen, argon, nitrogen, hydrogen chloride, water vapor,methane, and so on. Hydrogen anneals at 1100° C. are known to reducesurface roughness in silicon. By having a plasma, the temperaturerequirement can be reduced to less than approximately 400° C.

Alternatively, according to another embodiment of this presentinvention, a thin film, such as, for example, a Silicon oxide orphotosensitive resist, may be deposited atop the cleaved surface of thewafer or substrate and etched back. The etchant required for thisetch-back process may have approximately equal etch rates for bothsilicon and the deposited thin film. This etchant could reducenon-planarities on the wafer surface.

Alternatively, Gas Cluster Ion Beam technology may be utilized forsmoothing surfaces after cleaving along an implanted plane of hydrogenor other atomic species.

FIG. 143A-D shows a description of a prior art shallow trench isolationprocess. The process flow for the silicon chip could include thefollowing steps that occur in sequence from Step (A) to Step (D). Whenthe same reference numbers are used in different drawing figures (amongFIG. 143A-D), they indicate analogous, similar or identical structuresto enhance the understanding of the embodiments of the present inventionbeing discussed by clarifying the relationships between the structuresand embodiments presented in the various diagrams—particularly inrelating analogous, similar or identical functionality to differentphysical structures.

Step (A) is illustrated in FIG. 143A. A silicon wafer 14302 may beconstructed.

Step (B) is illustrated in FIG. 143B. A layer of silicon nitride 14306may be formed using a process such as chemical vapor deposition (CVD)and may then be lithographically patterned. Following this, an etchprocess may be conducted to form trench 14310. The silicon regionremaining after these process steps is indicated as 14308. A siliconoxide (not shown) may be utilized as a stress relief layer between thesilicon nitride 14306 and silicon wafer 14302.

Step (C) is illustrated using FIG. 143C. A thermal oxidation processat >700° C. may be conducted to form oxide region 14312. The siliconnitride layer 14306 may prevent the silicon nitride covered surfaces ofsilicon region 14308 from becoming oxidized during this process.

Step (D) is illustrated in FIG. 143D. An oxide fill may be deposited,following which an anneal may be preferably done to densify thedeposited oxide. A chemical mechanical polish (CMP) may be conducted toplanarize the surface. Silicon nitride layer 14306 may be removed eitherwith a CMP process or with a selective etch, such as hot phosphoricacid. The oxide fill layer after the CMP process is indicated as 14314.

The prior art process described in FIG. 143A-D is prone to the drawbackof high temperature (>400° C.) processing which is not suitable for someembodiments of the present invention that involve 3D stacking ofcomponents such as junction-less transistors (JLT) and recessed channelarray transistors (RCAT). Steps that involve temperatures greater than400° C. include the thermal oxidation conducted to form region 14312 andthe densification anneal conducted in Step (D) above.

FIG. 144A-D describes an embodiment of this present invention, wheresub-400° C. process steps are utilized to form the shallow trenchisolation regions. The process flow for the silicon chip may include thefollowing steps that occur in sequence from Step (A) to Step (D). Whenthe same reference numbers are used in different drawing figures (amongFIG. 144A-D), they are used to indicate analogous, similar or identicalstructures to enhance the understanding of the present invention byclarifying the relationships between the structures and embodimentspresented in the various diagrams—particularly in relating analogous,similar or identical functionality to different physical structures.

Step (A) is illustrated in FIG. 144A. A silicon wafer 14402 may beconstructed.

Step (B) is illustrated in FIG. 144B. A layer of silicon nitride 14406may be formed using a process, such as, for example, plasma-enhancedchemical vapor deposition (PECVD) or physical vapor deposition (PVD),and may then be lithographically patterned. Following this formation, anetch process may be conducted to form trench 14410. The silicon regionremaining after these process steps is indicated as 14408. A siliconoxide (not shown) may be utilized as a stress relief layer between thesilicon nitride 14406 and silicon wafer 14402.

Step (C) is illustrated in FIG. 144C. A plasma-assisted radical thermaloxidation process, which has a process temperature typically less thanapproximately 400° C., may be conducted to form the oxide region 14412.The silicon nitride layer 14406 may prevent the silicon nitride coveredsurfaces of silicon region 14308 from becoming oxidized during thisprocess.

Step (D) is illustrated using FIG. 144D. An oxide fill may be deposited,preferably using a process such as, for example, a high-density plasma(HDP) process that produces dense oxide layers at low temperatures, lessthan approximately 400° C. Depositing a dense oxide avoids therequirement for a densification anneal that would need to be conductedat a temperature greater than 400° C. A chemical mechanical polish (CMP)may be conducted to planarize the surface. Silicon nitride layer 14406may be removed either with a CMP process or with a selective etch, suchas hot phosphoric acid. The oxide fill layer after the CMP process isindicated as 14414.

The process described using FIG. 144A-D can be conducted at less than400° C., and this is advantageous for many 3D stacked architectures.

Lithography costs for semiconductor manufacturing today form a dominantpercentage of the total cost of a processed wafer. In fact, someestimates describe lithography cost as being more than 50% of the totalcost of a processed wafer. Thus, there is a need for the reduction oflithography cost for semiconductor manufacturing.

FIG. 145A-J describes an embodiment of the present invention, where aprocess flow is described in which a single lithography step is sharedamong many wafers. Although the process flow is described with respectto a junction-less transistor, it will be obvious to one with ordinaryskill in the art that it can be modified and applied to other types oftransistors, such as, for example, FINFETs and planar CMOS MOSFETs. Theprocess flow for the silicon chip may include the following steps thatoccur in sequence from Step (A) to Step (I). When the same referencenumbers are used in different drawing figures (among FIG. 145A-J), theyare used to indicate analogous, similar or identical structures toenhance the understanding of the embodiments of the present invention byclarifying the relationships between the structures and embodimentspresented in the various diagrams—particularly in relating analogous,similar or identical functionality to different physical structures.

Step (A) is illustrated in FIG. 145A. A p− Silicon wafer 14502 is taken.

Step (B) is illustrated in FIG. 145B. N+ and p+ dopant regions may beimplanted into the p− Silicon wafer 14502 of FIG. 145A. A thermalanneal, such as, for example, rapid, furnace, spike, or laser may thenbe done to activate dopants. Following this, a lithography and etchprocess may be conducted to define p− silicon region 14504 and n+silicon region 14506. Regions with p+ silicon where p-JLTs arefabricated are not shown.

Step (C) is illustrated in FIG. 145C. Gate dielectric regions 14510 andgate electrode regions 14508 may be formed by oxidation or deposition ofa gate dielectric, then deposition of a gate electrode, polishing withCMP and then lithography and etch. The gate electrode regions 14508 arepreferably doped polysilicon. Alternatively, various hi-k metal gate(HKMG) materials could be utilized for gate dielectric and gateelectrode as described previously.

Step (D) is illustrated in FIG. 145D. Silicon dioxide regions 14512 maybe formed by deposition and may then be planarized and polished with CMPsuch that the silicon dioxide regions 14512 cover p− silicon regions14504, n+ silicon regions 14506, gate electrode regions 14508 and gatedielectric regions 14510.

Step (E) is illustrated in FIG. 145E. The structure shown in FIG. 145Dmay be further polished with CMP such that portions of oxide regions14512, gate electrode regions 14508, gate dielectric regions 14510 andn+ silicon regions 14506 are polished. Following this polish, a silicondioxide layer may be deposited over the structure.

Step (F) is illustrated in FIG. 145F. Hydrogen H+ may be implanted intothe structure at a certain depth creating hydrogen plane 14514 indicatedby dotted lines.

Step (G) is illustrated in FIG. 145G. A silicon wafer 14518 may have asilicon dioxide layer 14516 deposited atop it.

Step (H) is illustrated in FIG. 145H. The structure shown in FIG. 145Gmay be flipped and bonded atop the structure shown in FIG. 145F usingoxide-to-oxide bonding.

Step (I) is illustrated in FIG. 145I and FIG. 145J. The structure shownin FIG. 145H may be cleaved at hydrogen plane 14514 using a sidewaysmechanical force. Alternatively, a thermal anneal, such as, for example,furnace or spike, could be used for the cleave process. Following thecleave process, CMP steps may be done to planarize surfaces. FIG. 145Ishows silicon wafer 14518 having an oxide layer 14516 and patternedfeatures transferred atop it. These patterned features may include gatedielectric regions 14524, gate electrode regions 14522, n+ siliconchannel 14520 and silicon dioxide regions 14526. These patternedfeatures may be used for further fabrication, with contacts,interconnect levels and other steps of the fabrication flow beingcompleted. FIG. 145J shows the substrate 14504 having patternedtransistor layers. These patterned transistor layers include gatedielectric regions 14532, gate electrode regions 14530, n+ siliconregions 14528 and silicon dioxide regions 14534. The structure in FIG.145J may be used for transferring patterned layers to other substratessimilar to the one shown in FIG. 145G using processes similar to thosedescribed in FIG. 145F-J. For example, a set of patterned featurescreated with lithography steps once (such as the one shown in FIG. 145E)may be layer transferred to many wafers, thereby removing therequirement for separate lithography steps for each wafer. Lithographycost can be reduced significantly using this approach.

Implanting hydrogen through the gate dielectric region 14510 in FIG.145F may not degrade the dielectric quality, since the area exposed toimplant species is small (a gate dielectric is typically 2 nm thick, andthe channel length is typically<20 nm, so the exposed area to theimplant species is just 40 sq. nm). Additionally, a thermal anneal oroxidation after the cleave may repair the potential implant damage.Also, a post-cleave CMP polish to remove the hydrogen rich plane withinthe gate dielectric may be performed.

An alternative embodiment of this present invention may involve forminga dummy gate transistor structure, as previously described for thereplacement gate process, for the structure shown in FIG. 145I. Postcleave, the gate electrode material 14522 and the gate dielectricmaterial 14524 may be etched away and then the trench may be filled witha replacement gate dielectric and a replacement gate electrode.

In an alternative embodiment of the invention described in FIG. 145A-J,the substrate 14518 in FIG. 145A-J may be a wafer with one or morepre-fabricated transistor and interconnect layers. Low temperature (lessthan approximately 400° C.) bonding and cleave techniques as previouslydescribed may be employed. In that scenario, 3D stacked logic chips maybe formed with fewer lithography steps. Alignment schemes similar tothose described previously may be used.

FIG. 146A-K describes an alternative embodiment of this presentinvention, wherein a process flow is described in which a Finfet isformed with lithography steps shared among many wafers. The process flowfor the silicon chip may include the following steps that occur insequence from Step (A) to Step (J). When the same reference numbers areused in different drawing figures (among FIG. 146A-K), they are used toindicate analogous, similar or identical structures to enhance theunderstanding of the embodiments of the present invention by clarifyingthe relationships between the structures and embodiments presented inthe various diagrams—particularly in relating analogous, similar oridentical functionality to different physical structures.

Step (A) is illustrated in FIG. 146A. An n− Silicon wafer 14602 istaken.

Step (B) is illustrated in FIG. 146B. P type dopant, such as, forexample, Boron ions, may be implanted into the n− Silicon wafer 14602 ofFIG. 146A. A thermal anneal, such as, for example, rapid, furnace,spike, or laser may then be done to activate dopants. Following this, alithography and etch process may be conducted to define n− siliconregion 14604 and p− silicon region 14690. Regions with n− silicon,similar in structure and formation to p− silicon region 14690, wherep-finfets are fabricated, are not shown.

Step (C) is illustrated in FIG. 146C. Gate dielectric regions 14610 andgate electrode regions 14608 may be formed by oxidation or deposition ofa gate dielectric, then deposition of a gate electrode, polishing withCMP, and then lithography and etch. The gate electrode regions 14608 maybe, for example, doped polysilicon. Alternatively, various hi-k metalgate (HKMG) materials could be utilized for gate dielectric and gateelectrode as described previously. N+ dopants, such as, for example,Arsenic, Antimony or Phosphorus, may then be implanted to form sourceand drain regions of the Finfet. The n+ doped source and drain regionsare indicated as 14606. FIG. 146D shows a cross-section of FIG. 146Calong the AA′ direction. P− doped region 14698 can be observed, as wellas n+ doped source and drain regions 14606, gate dielectric region14610, gate electrode region 14608, and n− silicon region 14604.

Step (D) is illustrated in FIG. 146E. Silicon dioxide regions 14612 maybe formed by deposition and may then be planarized and polished with CMPsuch that the silicon dioxide regions 14612 cover n+ silicon regions14604, n+ doped source and drain regions 14606, gate electrode region14608, p− doped region 14698, and gate dielectric region 14610.

Step (E) is illustrated in FIG. 146F. The structure shown in FIG. 146Emay be further polished with CMP such that portions of oxide regions14612, gate electrode regions 14608, gate dielectric regions 14610, p−doped silicon regions 14698, and n+ doped source and drain regions 14606are polished. Following this, a silicon dioxide layer may be depositedover the structure.

Step (F) is illustrated in FIG. 146G. Hydrogen H+ may be implanted intothe structure at a certain depth creating hydrogen plane 14614 indicatedby dotted lines.

Step (G) is illustrated in FIG. 146H. A silicon wafer 14618 may have asilicon dioxide layer 14616 deposited atop it.

Step (H) is illustrated in FIG. 146I. The structure shown in FIG. 146Hmay be flipped and bonded atop the structure shown in FIG. 145G usingoxide-to-oxide bonding.

Step (I) is illustrated in FIG. 146J and FIG. 146K. The structure shownin FIG. 146J may be cleaved at hydrogen plane 14614 using a sidewaysmechanical force. Alternatively, a thermal anneal, such as, for example,furnace or spike, could be used for the cleave process. Following thecleave process, CMP processes may be done to planarize surfaces. FIG.146J shows silicon wafer 14618 having an oxide layer 14616 and patternedfeatures transferred atop it. These patterned features may include gatedielectric regions 14624, gate electrode regions 14622, n+ siliconregion 14620, p− silicon region 14696 and silicon dioxide regions 14626.These patterned features may be used for further fabrication, withcontacts, interconnect levels and other steps of the fabrication flowbeing completed. FIG. 146K shows the substrate 14604 having patternedtransistor layers. These patterned transistor layers include gatedielectric regions 14632, gate electrode regions 14630, n+ siliconregions 14628 and silicon dioxide regions 14634. The structure in FIG.146K may be used for transferring patterned layers to other substratessimilar to the one shown in FIG. 146H using processes similar to thosedescribed in FIG. 146G-K. For example, a set of patterned featurescreated with lithography steps once (such as the one shown in FIG. 146F)may be layer transferred to many wafers, thereby removing therequirement for separate lithography steps for each wafer. Lithographycost can be reduced significantly using this approach.

Implanting hydrogen through the gate dielectric region 14610 in FIG.146G may not degrade the dielectric quality, since the area exposed toimplant species is small (a gate dielectric is typically 2 nm thick, andthe channel length is typically<20 nm, so the exposed area to theimplant species is just 40 sq. nm). Additionally, a thermal anneal oroxidation after the cleave may repair the potential implant damage.Also, a post-cleave CMP polish to remove the hydrogen rich plane withinthe gate dielectric may be performed.

An alternative embodiment of this present invention may involve forminga dummy gate transistor structure, as previously described for thereplacement gate process, for the structure shown in FIG. 146J. Postcleave, the gate electrode material 14622 and the gate dielectricmaterial 14624 may be etched away and then the trench may be filled witha replacement gate dielectric and a replacement gate electrode.

In an alternative embodiment of the invention described in FIG. 146A-K,the substrate 14618 in FIG. 146A-K may be a wafer with one or morepre-fabricated transistor and interconnect layers. Low temperature (lessthan approximately 400° C.) bonding and cleave techniques as previouslydescribed may be employed. In that scenario, 3D stacked logic chips maybe formed with fewer lithography steps. Alignment schemes similar tothose described previously may be used.

FIG. 147A-G describe another embodiment of the present invention as aprocess flow in which a planar transistor is formed with lithographysteps shared among many wafers. The process flow for the silicon chipmay include the following steps that occur in sequence from Step (A) toStep (F). When the same reference numbers are used in different drawingfigures (among FIG. 147A-G), they are used to indicate analogous,similar or identical structures to enhance the understanding of theembodiments of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams—particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A) is illustrated in FIG. 147A. A p− silicon wafer 14702 is taken.

Step (B) is illustrated in FIG. 147B. An n well implant opening may belithographically defined and n type dopants, such as, for example,Arsenic or Phosphorous, may be ion implanted into the p− silicon wafer14702. A thermal anneal, such as, for example, rapid, furnace, spike, orlaser may be done to activate the implanted dopants. Thus, n-well region14704 may be formed.

Step (C) is illustrated in FIG. 147C. Shallow trench isolation regions14706 may be formed, after which an oxide layer 14708 may be grown ordeposited. Following this, hydrogen H+ ions may be implanted into thewafer at a certain depth creating hydrogen plane 14710 indicated bydotted lines.

Step (D) is illustrated in FIG. 147D. A silicon wafer 14712 is taken andan oxide layer 14714 may be deposited or grown atop it.

Step (E) is illustrated in FIG. 147E. The structure shown in FIG. 147Cmay be flipped and bonded atop the structure shown in FIG. 147D usingoxide-to-oxide bonding of layers 14714 and 14708.

Step (F) is illustrated in FIG. 147F and FIG. 147G. The structure shownin FIG. 147E may be cleaved at hydrogen plane 14710 using a sidewaysmechanical force. Alternatively, a thermal anneal, such as, for example,furnace or spike, could be used for the cleave process. Following thecleave process, CMP processes may be used to planarize and polishsurfaces of both silicon wafers 14712 and 14732. FIG. 147F shows asilicon-on-insulator wafer formed after the cleave and CMP process wherep type regions 14716, n type regions 14718 and shallow trench isolationregions 14720 are formed atop oxide regions 14708 and 14714 and siliconwafer 14712. Transistor fabrication may then be completed on thestructure shown in FIG. 147F, following which metal interconnects may beformed. FIG. 147G shows wafer 14732 formed after the cleave and CMPprocess which includes p− silicon regions 14722, n well region 14724 andshallow trench isolation regions 14726. These features may be layertransferred to other wafers similar to the one shown in FIG. 147D usingprocesses similar to those shown in FIG. 147E-G. For example, a singleset of patterned features created with lithography steps once may belayer transferred onto many wafers thereby saving lithography cost.

In an alternative embodiment of the invention described in FIG. 147A-G,the substrate 14712 in FIG. 147A-G may be a wafer with one or morepre-fabricated transistor and metal interconnect layers. Low temperature(less than approximately 400° C.) bonding and cleave techniques aspreviously described may be employed. In that scenario, 3D stacked logicchips may be formed with fewer lithography steps. Alignment schemessimilar to those described previously may be used.

FIG. 148A-H describes another embodiment of this present invention,wherein 3D integrated circuits are formed with fewer lithography steps.The process flow for the silicon chip may include the following stepsthat occur in sequence from Step (A) to Step (G). When the samereference numbers are used in different drawing figures (among FIG.148A-I), they are used to indicate analogous, similar or identicalstructures to enhance the understanding of the present invention byclarifying the relationships between the structures and embodimentspresented in the various diagrams—particularly in relating analogous,similar or identical functionality to different physical structures.

Step (A) is illustrated in FIG. 148A. A p silicon wafer may have n typesilicon wells formed in it using standard procedures following which ashallow trench isolation may be formed. 14804 denotes p silicon regions,14802 denotes n silicon regions and 14898 denotes shallow trenchisolation regions.

Step (B) is illustrated in FIG. 148B. Dummy gates may be constructedwith silicon dioxide and polycrystalline silicon (polysilicon). The term“dummy gates” is used since these gates will be replaced by high k gatedielectrics and metal gates later in the process flow, according to thestandard replacement gate (or gate-last) process. This replacement gateprocess may also be called a gate replacement process. Further detailsof replacement gate processes are described in “A 45 nm Logic Technologywith High-k+Metal Gate Transistors, Strained Silicon, 9 Cu InterconnectLayers, 193 nm Dry Patterning, and 100% Pb-free Packaging,” IEDM Tech.Dig., pp. 247-250, 2007 by K. Mistry, et al. and “Ultralow-EOT (5 Å)Gate-First and Gate-Last High Performance CMOS Achieved byGate-Electrode Optimization,” IEDM Tech. Dig., pp. 663-666, 2009 by L.Ragnarsson, et al. 14806 and 14810 may be polysilicon gate electrodeswhile 14808 and 14812 may be silicon dioxide dielectric layers.

Step (C) is illustrated in FIG. 148C. The remainder of the gate-lasttransistor fabrication flow up to just prior to gate replacement mayproceed with the formation of source-drain regions 14814, strainenhancement layers to improve mobility (not shown), high temperatureanneal to activate source-drain regions 14814, formation of inter-layerdielectric (ILD) 14816, and so forth.

Step (D) is illustrated in FIG. 148D. Hydrogen may be implanted into thewafer creating hydrogen plane 14818 indicated by dotted lines.

Step (E) is illustrated in FIG. 148E. The wafer after step (D) may bebonded to a temporary carrier wafer 14820 using a temporary bondingadhesive 14822. This temporary carrier wafer 14820 may be constructed ofglass. Alternatively, it could be constructed of silicon. The temporarybonding adhesive 14822 may be a polymeric material, such as a polyimide.A thermal anneal or a sideways mechanical force may be utilized tocleave the wafer at the hydrogen plane 14818. A CMP process commences onthe exposed surface of p silicon region 14804. 14824 indicates a psilicon region, 14828 indicates an oxide isolation region and 14826indicates an n silicon region after this process.

FIG. 148F shows the other portion of the cleaved structure after a CMPprocess. 14834 indicates a p silicon region, 14830 indicates an nsilicon region and 14832 indicates an oxide isolation region. Thestructure shown in FIG. 148F may be reused to transfer layers usingprocess steps similar to those described with FIG. 148A-E to formstructures similar to FIG. 148E. This may enable a significant reductionin lithography cost.

Step (F) is illustrated in FIG. 148G: An oxide layer 14838 may bedeposited onto the bottom of the wafer shown in Step (E). The wafer maythen be bonded to the top surface of bottom layer of wires andtransistors 14836 using oxide-to-oxide bonding. The bottom layer ofwires and transistors 14836 could also be called a base wafer. Thetemporary carrier wafer 14820 may then be removed by shining a laseronto the temporary bonding adhesive 14822 through the temporary carrierwafer 14820 (which could be constructed of glass). Alternatively, athermal anneal could be used to remove the temporary bonding adhesive14822. Through-silicon connections 14842 with a non-conducting (e.g.oxide) liner 14844 to the landing pads 14840 in the base wafer may beconstructed at a very high density using special alignment methods to bedescribed in FIG. 26A-D and FIG. 27A-F.

Step (G) is illustrated in FIG. 148H. Dummy gates consisting of gateelectrodes 14808 and 14810 and gate dielectrics 14806 and 14812 may beetched away, followed by the construction of a replacement with high kgate dielectrics 14890 and 14894 and metal gates 14892 and 14896. Forexample, partially-formed high performance transistors are layertransferred atop the base wafer (may also be called target wafer)followed by the completion of the transistor processing with a low (sub400° C.) process. The remainder of the transistor, contact, and wiringlayers may then be constructed.

It will be appreciated by persons of ordinary skill in the art thatalternative versions of this flow are possible with various methods toattach temporary carriers and with various versions of the gate-last, orreplacement gate, process flow.

FIGS. 9A through 9C illustrates alternative configurations forthree-dimensional—3D integration of multiple dies constructing IC systemand utilizing Through Silicon Via. FIG. 9A illustrates an example inwhich the Through Silicon Via is continuing vertically throughsubstantially all the dies constructing a global cross-die connection.

FIG. 9B provides an illustration of similar sized dies constructing a 3Dsystem. FIG. 9B shows that the Through Silicon Via 404 is at the samerelative location in substantially all the dies constructing a standardinterface.

FIG. 9C illustrates a 3D system with dies having different sizes. FIG.9C also illustrates the use of wire bonding from substantially all threedies in connecting the IC system to the outside.

FIG. 10A is a drawing illustration of a continuous array wafer of aprior art U.S. Pat. No. 7,337,425. The bubble 102 shows the repeatingtile of the continuous array, and the lines 104 are the horizontal andvertical potential dicing lines. The tile 102 could be constructed as inFIG. 10B 102-1 with potential dicing line 104-1 or as in FIG. 10C withSerDes Quad 106 as part of the tile 102-2 and potential dicing lines104-2.

In general logic devices comprise varying quantities of logic elements,varying amounts of memories, and varying amounts of I/O. The continuousarray of the prior art allows defining various die sizes out of the samewafers and accordingly varying amounts of logic, but it is far moredifficult to vary the three-way ratio between logic, I/O, and memory. Inaddition, there exists different types of memories such as SRAM, DRAM,Flash, and others, and there exist different types of I/O such asSerDes. Some applications might need still other functions likeprocessor, DSP, analog functions, and others.

Embodiments of the present invention may enable a different approach.Instead of trying to put substantially all of these different functionsonto one programmable die, which will need a large number of veryexpensive mask sets, it uses Through-Silicon Via to constructconfigurable systems. The technology of “Package of integrated circuitsand vertical integration” has been described in U.S. Pat. No. 6,322,903issued to Oleg Siniaguine and Sergey Savastiouk on Nov. 27, 2001.

Accordingly embodiments of the present invention may suggest the use ofa continuous array of tiles focusing each one on a single, or very fewtypes of, function. Then, it constructs the end-system by integratingthe desired amount from each type of tiles, in a 3D IC system.

FIG. 11A is a drawing illustration of one reticle site on a wafercomprising tiles of programmable logic 1100A denoted FPGA. Such wafer isa continuous array of programmable logic. 1102 are potential dicinglines to support various die sizes and the amount of logic to beconstructed from one mask set. This die could be used as a base 1202A,1202B, 1202C or 1202D of the 3D system as in FIG. 12. In one alternativeof this present invention these dies may carry mostly logic, and thedesired memory and I/O may be provided on other dies, which may beconnected by means of Through-Silicon Via. It should be noted that insome cases it will be desired not to have metal lines, even if unused,in the dicing streets 108. In such case, at least for the logic dies,one may use dedicated masks to allow connection over the unusedpotential dicing lines to connect the individual tiles according to thedesired die size. The actual dicing lines are also called streets.

It should be noted that in general the lithography over the wafer isdone by repeatedly projecting what is named reticle over the wafer in a“step-and-repeat” manner. In some cases it might be preferable toconsider differently the separation between repeating tile 102 within areticle image vs. tiles that relate to two projections. For simplicitythis description will use the term wafer but in some cases it will applyonly to tiles with one reticle.

The repeating tile 102 could be of various sizes. For FPGA applicationsit may be reasonable to assume tile 1101 to have an edge size between0.5 mm to 1 mm which allows good balance between the end-device size andacceptable relative area loss due to the unused potential dice lines1102.

There are many advantages for a uniform repeating tile structure of FIG.11A where a programmable device could be constructed by dicing the waferto the desired size of programmable device. Yet it is still helpful thatthe end-device act as a complete integrated device rather than just as acollection of individual tiles 1101. FIG. 36 illustrates a wafercarrying an array of tiles 3601 with potential dice lines 3602 to bediced along actual dice lines 3612 to construct an end-device 3611 of3×3 tiles. The end device 3611 is bounded by the actual dice lines 3612.

FIG. 37 is a drawing illustration of an end-device 3611 comprising 9tiles 3701 such as 3601. Each tile 3701 contains a tiny micro controlunit—MCU 3702. The micro control unit could have a common architecturesuch as an 8051 with its own program memory and data memory. The MCUs ineach tile will be used to load the FPGA tile 3701 with its programmedfunction and substantially all its needed initialization for properoperation of the device. The MCU of each tile is connected so to becontrolled by the tile west of it or the tile south of it, in that orderof priority. So, for example, the MCU 3702-11 will be controlled by MCU3702-01. The MCU 3702-01 has no MCU west of it so it will be controlledby the MCU south of it 3702-00. Accordingly the MCU 3702-00 which is insouth-west corner has no tile MCU to control it and it will therefore bethe master control unit of the end-device.

FIG. 38 illustrates a simple control connectivity utilizing a slightlymodified Joint Test Action Group (JTAG)—based MCU architecture tosupport such a tiling approach. Each MCU has two Time-Delay-Integration(TDI) inputs, TDI 3816 from the device on its west side and TDIb 3814from the MCU on its south side. As long as the input from its west sideTDI 3816 is active it will be the controlling input, otherwise the TDIb3814 from the south side will be the controlling input. Again in thisillustration the Tile at the south-west corner 3800 will take control asthe master. Its control inputs 3802 would be used to control theend-device and through this MCU 3800 it will spread to substantially allother tiles. In the structure illustrated in FIG. 38 the outputs of theend-device 3611 are collected from the MCU of the tile at the north-eastcorner 3820 at the TDO output 3822. These MCUs and their connectivitywould be used to load the end-device functions, initialize it, test it,debug it, program its clocks, and substantially all other desiredcontrol functions. Once the end-device has completed its set up or othercontrol and initialization functions such as testing or debugging, theseMCUs could be then utilized for user functions as part of the end-deviceoperation.

An additional advantage for this construction of a tiled FPGA array withMCUs is in the construction of an SoC with embedded FPGA function. Asingle tile 3601 could be connected to an SoC using Through SiliconVias—TSVs and accordingly provides a self-contained embedded FPGAfunction.

Clearly, the same scheme can be modified to use the East/North (or anyother combination of orthogonal directions) to encode effectively anidentical priority scheme.

FIG. 11B is a drawing illustration of an alternative reticle site on awafer comprising tiles of Structured ASIC 1100B. Such wafer may be, forexample, a continuous array of configurable logic. 1102 are potentialdicing lines to support various die sizes and the amount of logic to beconstructed. This die could be used as a base 1202A, 1202B, 1202C or1202D of the 3D system as in FIG. 12.

FIG. 11C is a drawing illustration of another reticle site on a wafercomprising tiles of RAM 1100C. Such wafer may be a continuous array ofmemories. The die diced out of such wafer may be a memory die componentof the 3D integrated system. It might include an antifuse layer or otherform of configuration technique to function as a configurable memorydie. Yet it might be constructed as a multiplicity of memories connectedby a multiplicity of Through-Silicon Vias to the configurable die, whichmay also be used to configure the raw memories of the memory die to thedesired function in the configurable system.

FIG. 11D is a drawing illustration of another reticle site on a wafercomprising tiles of DRAM 1100D. Such wafer may be a continuous array ofDRAM memories.

FIG. 11E is a drawing illustration of another reticle site on a wafercomprising tiles of microprocessor or microcontroller cores 1100E. Suchwafer may be a continuous array of Processors.

FIG. 11F is a drawing illustration of another reticle site on a wafercomprising tiles of I/Os 1100F. This could include groups of SerDes.Such a wafer may be a continuous tile of I/Os. The die diced out of suchwafer may be an I/O die component of a 3D integrated system. It couldinclude an antifuse layer or other form of configuration technique suchas SRAM to configure these I/Os of the configurable I/O die to theirfunction in the configurable system. Yet it might be constructed as amultiplicity of I/O connected by a multiplicity of Through-Silicon Viasto the configurable die, which may also be used to configure the rawI/Os of the I/O die to the desired function in the configurable system.

I/O circuits are a good example of where it could be advantageous toutilize an older generation process. Usually, the process drivers areSRAM and logic circuits. It often takes longer to develop the analogfunction associated with I/O circuits, SerDes circuits, PLLs, and otherlinear functions. Additionally, while there may be an advantage to usingsmaller transistors for the logic functionality, I/Os may need strongerdrive and relatively larger transistors. Accordingly, using an olderprocess may be more cost effective, as the older process wafer mightcost less while still performing effectively.

An additional function that it might be advantageous to pull out of theprogrammable logic die and onto one of the other dies in the 3D system,connected by Through-Silicon-Vias, may be the Clock circuits and theirassociated PLL, DLL, and control. Clock circuits and distribution. Thesecircuits may often be area consuming and may also be challenging in viewof noise generation. They also could in many cases be more effectivelyimplemented using an older process. The Clock tree and distributioncircuits could be included in the I/O die. Additionally the clock signalcould be transferred to the programmable die using theThrough-Silicon-Vias (TSVs) or by optical means. A technique to transferdata between dies by optical means was presented for example in U.S.Pat. No. 6,052,498 assigned to Intel Corp.

Alternatively an optical clock distribution could be used. There are newtechniques to build optical guides on silicon or other substrates. Anoptical clock distribution may be utilized to minimize the power usedfor clock signal distribution and would enable low skew and low noisefor the rest of the digital system. Having the optical clock constructedon a different die and than connected to the digital die by means ofThrough-Silicon-Vias or by optical means make it very practical, whencompared to the prior art of integrating optical clock distribution withlogic on the same die.

Alternatively the optical clock distribution guides and potentially someof the support electronics such as the conversion of the optical signalto electronic signal could be integrated by using layer transfer andsmart cut approaches as been described before in FIGS. 14 and 20. Theoptical clock distribution guides and potentially some of the supportelectronics could be first built on the ‘Foundation’ wafer 1402 and thena thin layer 1404 may be transferred on top of it using the ‘smart cut’flow, so substantially all the following construction of the primarycircuit would take place afterward. The optical guide and its supportelectronics would be able to withstand the high temperatures necessaryfor the processing of transistors on layer 1404.

And as related to FIG. 20, the optical guide, and the propersemiconductor structures on which at a later stage the supportelectronics would be processed, could be pre-built on layer 2019. Usingthe ‘smart cut’ flow it would be then transferred on top of a fullyprocessed wafer 808. The optical guide should be able to withstand theion implant 2008 necessary for the ‘smart cut’ while the supportelectronics would be finalized in flows similar to the ones presented inFIGS. 21 to 35, and 39 to 94. This means that the landing target for theclock signal will need to accommodate the approximately 1 micronmisalignment of the transferred layer 2004 to the prefabricated-primarycircuit and its upper layer 808. Such misalignment could be acceptablefor many designs. Alternatively only the base structure for the supportelectronics would be pre-fabricated on layer 2019 and the optical guidewill be constructed after the layer transfer along with finalized flowsof the support electronics using flows similar to the ones presented inrelating to FIGS. 21-35, and 39 to 94. Alternatively, the supportelectronics could be fabricated on top of a fully processed wafer 808 byusing flows similar to the ones presented in relating to FIGS. 21-35,and 39 to 94. Then an additional layer transfer on top of the supportelectronics would be utilized to construct the optical wave guides atlow temperature.

Having wafers dedicated to each of these functions may support highvolume generic product manufacturing. Then, similar to Lego® blocks,many different configurable systems could be constructed with variousamounts of logic memory and I/O. In addition to the alternativespresented in FIGS. 11A through 11F there many other useful functionsthat could be built and that could be incorporated into the 3DConfigurable System. Examples of such may be image sensors, analog, dataacquisition functions, photovoltaic devices, non-volatile memory, and soforth.

An additional function that would fit well for 3D systems using TSVs, asdescribed, is a power control function. In many cases it is desired toshut down power at times to a portion of the IC that is not currentlyoperational. Using controlled power distribution by an external dieconnected by TSVs is advantageous as the power supply voltage to thisexternal die could be higher because it is using an older process.Having a higher supply voltage allows easier and better control of powerdistribution to the controlled die.

Those components of configurable systems could be built by one vendor,or by multiple vendors, who agree on a standard physical interface toallow mix-and-match of various dies from various vendors.

The construction of the 3D Programmable System could be done for thegeneral market use or custom-tailored for a specific customer.

Another advantage of some embodiments of this present invention may bean ability to mix and match various processes. It might be advantageousto use memory from a leading edge process, while the I/O, and maybe ananalog function die, could be used from an older process of maturetechnology (e.g., as discussed above).

FIGS. 12A through 12E illustrate integrated circuit systems. Anintegrated circuit system that comprises configurable die could becalled a Configurable System. FIG. 12A through 12E are drawingsillustrating integrated circuit systems or Configurable Systems withvarious options of die sizes within the 3D system and alignments of thevarious dies. FIG. 12E presents a 3D structure with some lateraloptions. In such case a few dies 1204E, 1206E, 1208E are placed on thesame underlying die 1202E allowing relatively smaller die to be placedon the same mother die. For example die 1204E could be a SerDes diewhile die 1206E could be an analog data acquisition die. It could beadvantageous to fabricate these die on different wafers using differentprocess and than integrate them in one system. When the dies arerelatively small then it might be useful to place them side by side(such as FIG. 12E) instead of one on top of the other (FIGS. 12A-D).

The Through Silicon Via technology is constantly evolving. In the earlygenerations such via would be 10 microns in diameter. Advanced work isnow demonstrating Through Silicon Via with less than a 1-microndiameter. Yet, the density of connections horizontally within the diemay typically still be far denser than the vertical connection usingThrough Silicon Via.

In another alternative of the present invention the logic portion couldbe broken up into multiple dies, which may be of the same size, to beintegrated to a 3D configurable system. Similarly it could beadvantageous to divide the memory into multiple dies, and so forth, withother function.

Recent work on 3D integration shows effective ways to bond waferstogether and then dice those bonded wafers. This kind of assembly maylead to die structures like FIG. 12A or FIG. 12D. Alternatively for some3D assembly techniques it may be better to have dies of different sizes.Furthermore, breaking the logic function into multiple verticallyintegrated dies may be used to reduce the average length of some of theheavily loaded wires such as clock signals and data buses, which may, inturn, improve performance.

An additional variation of the present invention may be the adaptationof the continuous array (presented in relation to FIGS. 10 and 11) tothe general logic device and even more so for the 3D IC system.Lithography limitations may pose considerable concern to advanced devicedesign. Accordingly regular structures may be highly desirable andlayers may be constructed in a mostly regular fashion and in most caseswith one orientation at a time. Additionally, highlyvertically-connected 3D IC system could be most efficiently constructedby separating logic memories and I/O into dedicated layers. For alogic-only layer, the structures presented in FIG. 76 or FIG. 78 couldbe used extensively, as illustrated in FIG. 84. In such a case, therepeating logic pattern 8402 could be made full reticle size. FIG. 84Aillustrates a repeating pattern of the logic cells of FIG. 78B whereinthe logic cell is repeating 8×12 times. FIG. 84B illustrates the samelogic repeating many more times to fully fill a reticle. The multiplemasks used to construct the logic terrain could be used for multiplelogic layers within one 3D IC and for multiple ICs. Such a repeatingstructure could comprise the logic P and N transistors, theircorresponding contact layers, and even the landing strips for connectingto the underlying layers. The interconnect layers on top of these logicterrain could be made custom per design or partially custom depending onthe design methodology used. The custom metal interconnect may leave thelogic terrain unused in the dicing streets area. Alternatively adicing-streets mask could be used to etch away the unused transistors inthe streets area 8404 as illustrated in FIG. 84C.

The continuous logic terrain could use any transistor style includingthe various transistors previously presented. An additional advantage tosome of the 3D layer transfer techniques previously presented may be theoption to pre-build, in high volume, transistor terrains for furtherreduction of 3D custom IC manufacturing costs.

Similarly a memory terrain could be constructed as a continuousrepeating memory structure with a fully populated reticle. Thenon-repeating elements of most memories may be the address decoder andsome times the sense circuits. Those non repeating elements may beconstructed using the logic transistors of the underlying or overlyinglayer.

FIGS. 84D-G are drawing illustrations of an SRAM memory terrain. FIG.84D illustrates a conventional 6 transistor SRAM cell 8420 controlled byWord Line (WL) 8422 and Bit Lines (BL, BLB) 8424, 8426. Usually the SRAMbit cell is specially designed to be very compact.

The generic continuous array 8430 may be a reticle step field sizedterrain of SRAM bit cells 8420 wherein the transistor layers and eventhe Metal 1 layer may be used by substantially all designs. FIG. 84Eillustrates such continuous array 8430 wherein a 4×4 memory block 8432has been defined by etching the cells around it 8434. The memory may becustomized by custom metal masks such metal 2 and metal 3. To controlthe memory block the Word Lines 8438 and the Bit Lines 8436 may beconnected by through vias to the logic terrain underneath or above it.

FIG. 84F illustrates the logic structure 8450 that may be constructed onthe logic terrain to drive the Word Lines 8452. FIG. 84G illustrates thelogic structure 8460 that may be constructed on the logic terrain todrive the Bit Lines 8462. FIG. 84G also illustrates the read sensecircuit 8468 that may read the memory content from the bit lines 8462.In a similar fashion, other memory structures may be constructed fromthe uncommitted memory terrain using the uncommitted logic terrain closeto the intended memory structure. In a similar fashion, other types ofmemory, such as flash or DRAM, may comprise the memory terrain.Furthermore, the memory terrain may be etched away at the edge of theprojected die borders to define dicing streets similar to that indicatedin FIG. 84C for a logic terrain.

Constructing 3D ICs utilizing multiple layers of different function maycombine 3D layers using the layer transfer techniques according to someembodiments of the present invention, with fully prefabricated deviceconnected by industry standard TSV technique.

An additional aspect of the present invention may provide a yield repairfor random logic. The 3D IC techniques thus presented may allow theconstruction of a very complex logic 3D IC by using multiple layers oflogic. In such a complex 3D IC, enabling the repair of random defectscommon in IC manufacturing may be highly desirable. Repair of repeatingstructures is known and commonly used in memories and will be presentedin respect to FIG. 41. Another alternative is a repair for random logicleveraging the attributes of the presented 3D IC techniques and DirectWrite eBeam technology such as, for example, technologies offered byAdvantest, Fujitsu Microelectronics and Vistec.

FIG. 86A illustrates a 3D logic IC structured for repair. Theillustrated 3D logic IC may comprise three logic layers 8602, 8612, 8622and an upper layer of repair logic 8632. In each logic layersubstantially all primary outputs, the Flip Flop (FF) outputs, may befed to the upper layer 8632, the repair layer. The upper layer 8632initially may comprise a repeating structure of uncommitted logictransistors similar to those of FIGS. 76 and 78. The circuitry of logiclayer 8602 may be constructed on SOI wafers so that the performance oflogic layer 8602 may more closely match logic layers 8612, 8622 andrepair logic layer 8632.

FIG. 87 illustrates a Flip Flop designed for repairable 3D IC logic.Such Flip Flop 8702 may include, in addition to its normal output 8704,a branch 8706 going up to the top layer, and the repair logic layer8632. For each Flip Flop, two lines may originate from the top layer8632, namely, the repair input 8708 and the control 8710. The normalinput to the Flip Flop 8712 may go in through a multiplexer 8714designed to select the normal input 8712 as long as the top control 8710is floating. But once the top control 8710 is active low the multiplexer8714 may select the repair input 8708. A faulty input may impact morethan one primary input. The repair may then recreate substantially allthe necessary logic to replace substantially all the faulty inputs in asimilar fashion.

Multiple alternatives may exist for inserting the new input, includingthe use of programmability such as, for example, a one-time-programmableelement to switch the multiplexer 8714 from the original input 8712 tothe repaired input 8708 without the need of a top control wire 8710.

At the fabrication, the 3D IC wafer may go through a full scan test. Ifa fault is detected, a yield repair process would be applied. Using thedesign data base, repair logic may be built on the upper layer 8632. Therepair logic has access to substantially all the primary outputs as theyare all available on the top layer. Accordingly, those outputs neededfor the repair may be used in the reconstruction of the exact logicfound to be faulty. The reconstructed logic may include some enhancementsuch as drive size or metal wires strength to compensate for the longerlines going up and then down. The repair logic, as a de-factoreplacement of the faulty logic ‘cone,’ may be built using theuncommitted transistors on the top layer. The top layer may becustomized with a custom metal layer defined for each die on the waferby utilizing the direct write eBeam. The replacement signal 8708 may beconnected to the proper Flip Flop and become active by having the topcontrol signal 8710 active low.

The repair flow may also be used for performance enhancement. If thewafer test includes timing measurements, a slow performing logic ‘cone’could be replaced in a similar manner to a faulty logic ‘cone’ describedpreviously, e.g., in the preceding paragraph.

FIG. 86B is a drawing illustration of a 3D IC wherein the scan chainsare designed so each is confined to one layer. This confinement mayallow testing of each layer as it is fabricated and could be useful inmany ways. For example, after a circuit layer is completed and thentested showing very bad yield, then the wafer could be removed and notcontinued for building additional 3D circuit layers on top of bad base.Alternatively, a design may be constructed to be very modular andtherefore the next transferred circuit layer could comprise replacementmodules for the underlying faulty base layer similar to what wassuggested in respect to FIG. 41.

The elements of the present invention related to FIGS. 86A and 86B mayneed testing of the wafer during the fabrication phase, which might beof concern in respect to debris associated with making physical contactwith a wafer for testing if the wafer is probed when tested. FIG. 86C isa drawing illustration of an embodiment which provides for contact-lessautomated self-testing. A contact-less power harvesting element might beused to harvest the electromagnetic energy directed at the circuit ofinterest by a coil base antenna 86C02, an RF to DC conversion circuit86C04, and a power supply unit 86C06 to generate the necessary supplyvoltages to run the self-test circuits and the various 3D IC circuits86C08 to be tested. Alternatively, a tiny photo voltaic cell 86C10 couldbe used to convert light beam energy to electric current which will beconverted by the power supply unit 86C06 to the needed voltages. Oncethe circuits are powered, a Micro Control Unit 86C12 could perform afull scan test of all existing circuits 86C08. The self-test could befull scan or other BIST (Built In Self-Test) alternatives. The testresult could be transmitted using wireless radio module 86C14 to a baseunit outside of the 3D IC wafer. Such contact less wafer testing couldbe used for the test as was referenced in respect to FIG. 86A and FIG.86B or for other application such as wafer to wafer or die to waferintegration using TSVs. Alternative uses of contact-less testing couldbe applied to various combinations of the present invention. One exampleis where a carrier wafer method may be used to create a wafer transferlayer whereby transistors and the metal layers connecting them to formfunctional electronic circuits are constructed. Those functionalcircuits could be contact-lessly tested to validate proper yield, and,if appropriate, actions to repair or activate built-in redundancy may bedone. Then using layer transfer, the tested functional circuit layer maybe transferred on top of another processed wafer 808, and then beconnected be utilizing one of the approaches presented before.

According to the yield repair design methodology, substantially all theprimary outputs 8706 may go up and substantially all primary inputs 8712could be replaced by signals coming from the top 8708.

An additional advantage of this yield repair design methodology may bethe ability to reuse logic layers from one design to another design. Forexample, a 3D IC system may be designed wherein one of the layers maycomprise a WiFi transceiver receiver. And such circuit may now be neededfor a completely different 3D IC. It might be advantageous to reuse thesame WiFi transceiver receiver in the new design by just having thereceiver as one of the new 3D IC design layers to save the redesigneffort and the associated NRE (non recurring expense) for masks and etc.The reuse could be applied to many other functions, allowing the 3D ICto resemble the old way of integrating function—the PC (printed circuit)Board. For such a concept to work well, a connectivity standard for theconnection of wires up and down may be desirable.

Another application of these concepts could be the use of the upperlayer to modify the clock timing by adjusting the clock of the actualdevice and its various fabricated elements. Scan circuits could be usedto measure the clock skew and report it to an external design tool. Theexternal design tool could construct the timing modification that wouldbe applied by the clock modification circuits. A direct write ebeamcould then be used to form the transistors and circuitry on the toplayer to apply those clock modifications for a better yield andperformance of the 3D IC end product.

An alternative approach to increase yield of complex systems through useof 3D structure is to duplicate the same design on two layers verticallystacked on top of each other and use BIST techniques similar to thosedescribed in the previous sections to identify and replacemalfunctioning logic cones. This should prove particularly effectiverepairing very large ICs with very low yields at manufacturing stageusing one-time, or hard to reverse, repair structures such as, forexample, antifuses or Direct-Write e-Beam customization. Similar repairapproach can also assist systems that may need a self-healing ability atevery power-up sequence through use of memory-based repair structures asdescribed with regard to FIG. 114 below.

FIG. 114 is a drawing illustration of one possible implementation ofthis concept. Two vertically stacked logic layers 11401 and 11402implement, for example, an identical design. The circuitry of logiclayer 11401 may be constructed on SOI wafers so that the performance oflogic layer 11401 may more closely match logic layer 11402. The design(same on each layer) is scan-based and includes BIST Controller/Checkeron each layer 11451 and 11452 that can communicate with each othereither directly or through an external tester. 11421 is a representativeFlip-Flop (FF) on the first layer that has its corresponding FF 11422 onlayer 2, each fed by its respective identical logic cones 11411 and11412. The output of flip flop 11421 is coupled to the A input ofmultiplexer 11431 and the B input of multiplexer 11432 through verticalconnection 11406, while the output of flip flop 11422 is coupled to theA input of multiplexer 11432 and the B input of multiplexer 11431through vertical connection 11405. Each such output multiplexer isrespectively controlled from control points 11441 and 11442, andmultiplexer outputs drive the respective following logic stages at eachlayer. Thus, either logic cone 11411 and flip flop 11421 or logic cone11412 and flip flop 11422 may be either programmably coupleable orselectively coupleable to the following logic stages at each layer.

The multiplexer control points 11441 and 11442 can be implemented usinga memory cell, a fuse, an Antifuse, or any other customizable elementsuch as, for example, a metal link that can be customized by aDirect-Write e-Beam machine. If a memory cell is used, its contents canbe stored in a ROM, a flash memory, or in some other non-volatilestorage medium elsewhere in the 3D IC or in the system in which contentsare deployed and loaded upon a system power up, a system reset, oron-demand during system maintenance.

Upon power on, the BCC initializes all multiplexer controls to selectinputs A and runs diagnostic test on the design on each layer. FailingFlip Flops (FFs) are identified at each logic layer using scan and BISTtechniques, and as long as there is no pair of corresponding FF thatfails, the BCCs can communicate with each other (directly or through anexternal tester) to determine which working FF to use and program themultiplexer controls 11441 and 11442 accordingly.

If multiplexer controls 11441 and 11442 are reprogrammable with respectto using memory bit cells, such test and repair process can potentiallyoccur for every power on instance, or on demand, and the 3D IC canself-repair in-circuit. If the multiplexer controls are one-timeprogrammable, the diagnostic and repair process may need to be performedusing external equipment. It should be noted that the techniques forcontact-less testing and repair as previously described with regard toFIG. 86C can be applicable in this situation.

An alternative embodiment of this concept can use multiplexing 8714 atthe inputs of the FF such as described in FIG. 87. In that case both theQ and the inverted Q of FFs may be used, if present.

Person skilled in the art will appreciate that this repair technique ofselecting one of two possible outputs from two similar blocks verticallystacked on top of each other can be applied to other types of blocks inaddition to FF described above. Examples of such include, but are notlimited to, analog blocks, I/O, memory, and other blocks. In such casesthe selection of the working output may need specialized multiplexingbut the nature of the technique remains unchanged.

Such person will also appreciate that once the BIST diagnosis of bothlayers is complete, a mechanism similar to the one used to define themultiplexer controls can also be used to selectively power off unusedsections of a logic layers to save on power dissipation.

Yet another variation on the present invention is to use verticalstacking for on the fly repair using redundancy concepts such as Triple(or higher) Modular Redundancy (“TMR”). TMR is a well-known concept inthe high-reliability industry where three copies of each circuit aremanufactured and their outputs are channeled through a majority votingcircuitry. Such TMR system will continue to operate correctly as long asno more than a single fault occurs in any TMR block. A major problem indesigning TMR ICs is that when the circuitry is triplicated, theinterconnections become significantly longer which slows down the systemspeed, and the routing becomes more complex which slows down systemdesign. Another major problem for TMR is that its design process isexpensive because of correspondingly large design size, while its marketis limited.

Vertical stacking offers a natural solution of replicating the systemimage on top of each other. FIG. 115 illustrates such a system withthree layers 11501 11502 11503, where combinatorial logic is replicatedsuch as in logic cones 11511-1, 11511-2, and 11511-3, and FFs arereplicated such as 11521-1, 11521-2, and 11521-3. The circuitry of logiclayer 11501 may be constructed on SOI wafers so that the performance oflogic layer 11501 may more closely match logic layers 11502 and 11503.One of the layers, 11501 in this depiction, includes a majority votingcircuitry 11531 that arbitrates among the local FF output 11551 and thevertically stacked FF outputs 11552 and 11553 to produce a final faulttolerant FF output that needs to be distributed to all logic layers as11541-1, 11541-2, 11541-3.

Person skilled in the art will appreciate that variations on thisconfiguration are possible such as dedicating a separate layer just tothe voting circuitry that will make layers 11501, 11502 and 11503logically identical; relocating the voting circuitry to the input of theFFs rather than to its output; or extending the redundancy replicationto more than 3 instances (and stacked layers).

The above mentioned method for designing Triple Modular Redundancy (TMR)addresses both of the mentioned weaknesses. First, there is little or noadditional routing congestion in any layer because of TMR, and thedesign at each layer can be optimally implemented in a single imagerather than in triplicate. Second, any design implemented for nonhigh-reliability market can be converted to TMR design with minimaleffort by vertical stacking of three original images and adding amajority voting circuitry either to one of the layers as in FIG. 115, toall three layers, or as a separate layer. A TMR circuit can be shippedfrom the factory with known errors present (masked by the TMRredundancy), or a Repair Layer can be added to repair any known errorsfor an even higher degree of reliability.

The exemplary embodiments discussed so far are primarily concerned withyield enhancement and repair in the factory prior to shipping a 3D IC toa customer. Another aspect of the present invention is providingredundancy and self-repair once the 3D IC is deployed in the field. Thisis a desirable product characteristic because defects may occur inproducts tested as operating correctly in the factory. For example,defects can occur due to a delayed failure mechanism such as a defectivegate dielectric in a transistor that develops into a short circuitbetween the gate and the underlying transistor source, drain or body.Immediately after fabrication, such a transistor may function correctlyduring factory testing, but with time and applied voltages andtemperatures, the defect can develop into a failure which may bedetected during subsequent tests in the field. Many other delayedfailure mechanisms are known. Regardless of the nature of the delayeddefect, if it creates a logic error in the 3DIC then subsequent testingaccording to the present invention may be used to detect and repair it.

FIG. 119 illustrates an exemplary 3D IC generally indicated by 11900according to an embodiment of the present invention. 3D IC 11900includes two layers labeled Layer 1 and Layer 2 and separated by adashed line in the figure. Layer 1 and Layer 2 may be bonded togetherinto a single 3D IC using methods known in the art. The electricalcoupling of signals between Layer 1 and Layer 2 may be realized withThrough-Silicon Via (TSV) or some other interlayer technology. Layer 1and Layer 2 may each include a single layer of semiconductor devicescalled a Transistor Layer and its associated interconnections (typicallyrealized in one or more physical Metal Layers) which are calledInterconnection Layers. The combination of a Transistor Layer and one ormore Interconnection Layers is called a Circuit Layer. Layer 1 and Layer2 may each include one or more Circuit Layers of devices andinterconnections as a matter of design choice.

Despite differences in construction details, Layer 1 and Layer 2 in 3DIC 11900 perform substantially identical logic functions. In someembodiments, Layer 1 and Layer 2 may each be fabricated using the samemasks for all layers to reduce manufacturing costs. In otherembodiments, there may be small variations on one or more mask layers.For example, there may be an option on one of the mask layers whichcreates a different logic signal on each layer which tells the controllogic blocks on Layer 1 and Layer 2 that they are the controllers Layer1 and Layer 2 respectively in cases where this is important. Otherdifferences between the layers may be present as a matter of designchoice.

Layer 1 may include Control Logic 11910, representative scan flip-flops11911, 11912 and 11913, and representative combinational logic clouds11914 and 11915, while Layer 2 may include Control Logic 11920,representative scan flip-flops 11921, 11922 and 11923, andrepresentative logic clouds 11924 and 11925. Control Logic 11910 andscan flip-flops 11911, 11912 and 11913 are coupled together to form ascan chain for set scan testing of combinational logic clouds 11914 and11915 in a manner previously described. Control Logic 11920 and scanflip-flops 11921, 11922 and 11923 are also coupled together to form ascan chain for set scan testing of combinational logic clouds 11924 and11925. Control Logic blocks 11910 and 11920 are coupled together toallow coordination of the testing on both Layers. In some embodiments,Control Logic blocks 11910 and 11920 may test either themselves or eachother. If one of them is bad, the other can be used to control testingon both Layer 1 and Layer 2.

Persons of ordinary skill in the art will appreciate that the scanchains in FIG. 119 are representative only, that in a practical designthere may be millions of flip-flops which may broken into multiple scanchains, and the inventive principles disclosed herein apply regardlessof the size and scale of the design.

As with previously described embodiments, the Layer 1 and Layer 2 scanchains may be used in the factory for a variety of testing purposes. Forexample, Layer 1 and Layer 2 may each have an associated Repair Layer(not shown in FIG. 119) which was used to correct any defective logiccones or logic blocks which originally occurred on either Layer 1 orLayer 2 during their fabrication processes. Alternatively, a singleRepair Layer may be shared by Layer 1 and Layer 2.

FIG. 120 illustrates exemplary scan flip-flop 12000 (surrounded by thedashed line in the figure) suitable for use with some embodiments of thepresent invention. Scan flip-flop 12000 may be used for the scanflip-flop instances 11911, 11912, 11913, 11921, 11922 and 11923 in FIG.119. Present in FIG. 120 is D-type flip-flop 12002 which has a Q outputcoupled to the Q output of scan flip-flop 12000, a D input coupled tothe output of multiplexer 12004, and a clock input coupled to the CLKsignal. Multiplexer 12004 also has a first data input coupled to theoutput of multiplexer 12006, a second data input coupled to the SI (ScanInput) input of scan flip-flop 12000, and a select input coupled to theSE (Scan Enable) signal. Multiplexer 12006 has a first and second datainputs coupled to the D0 and D1 inputs of scan flip-flop 12000 and aselect input coupled to the LAYER_SEL signal.

The SE, LAYER_SEL and CLK signals are not shown as coupled to inputports on scan flip-flop 12000 to avoid over complicating thedisclosure—particularly in drawings like FIG. 119 where multipleinstances of scan flip-flop 12000 appear and explicitly routing themwould detract attention from the concepts being presented. In apractical design, all three of those signals are typically coupled to anappropriate circuit for every instance of scan flip-flop 12000.

When asserted, the SE signal places scan flip-flop 12000 into scan modecausing multiplexer 12004 to gate the SI input to the D input of D-typeflip-flop 12002. Since this signal goes to all scan flip-flops 12000 ina scan chain, thus connecting them together as a shift register allowingvectors to be shifted in and test results to be shifted out. When SE isnot asserted, multiplexer 12004 selects the output of multiplexer 12006to present to the D input of D-type flip-flop 12002.

The CLK signal is shown as an “internal” signal here since its originwill differ from embodiment to embodiment as a matter of design choice.In practical designs, a clock signal (or some variation of it) istypically routed to every flip-flop in its functional domain. In somescan test architectures, CLK will be selected by a third multiplexer(not shown in FIG. 120) from a domain clock used in functional operationand a scan clock for use in scan testing. In such cases, the SCAN_ENsignal will typically be coupled to the select input of the thirdmultiplexer so that D-type flip-flop 12002 will be correctly clocked inboth scan and functional modes of operation. In other scanarchitectures, the functional domain clock may be used as the scan clockduring test modes and no additional multiplexer is needed. Persons ofordinary skill in the art will appreciate that many different scanarchitectures are known and will realize that the particular scanarchitecture in any given embodiment will be a matter of design choiceand in no way limits the present invention.

The LAYER_SEL signal determines the data source of scan flip-flop 12000in normal operating mode. As illustrated in FIG. 119, input D1 iscoupled to the output of the logic cone of the Layer (either Layer 1 orLayer 2) where scan flip-flop 12000 is located, while input D0 iscoupled to the output of the corresponding logic cone on the otherLayer. The default value for LAYER_SEL is thus logic-1 which selects theoutput from the same Layer. Each scan flip-flop 12000 has its own uniqueLAYER_SEL signal. This allows a defective logic cone on one Layer to beprogrammably or selectively replaced by its counterpart on the otherLayer. In such cases, the signal coupled to D1 being replaced is calleda Faulty Signal while the signal coupled to D0 replacing it is called aRepair Signal.

FIG. 121A illustrates an exemplary 3D IC generally indicated by 12100.Like the embodiment of FIG. 119, 3D IC 12100 includes two Layers labeledLayer 1 and Layer 2 and separated by a dashed line in the drawingfigure. Layer 1 may include Layer 1 Logic Cone 12110, scan flip-flop12112, and XOR gate 12114, while Layer 2 may include Layer 2 Logic Cone12120, scan flip-flop 12122, and XOR gate 12124. The scan flip-flop12000 of FIG. 120 may be used for scan flip-flops 12112 and 12122,though the SI and other internal connections are not shown in FIG. 121A.The output of Layer 1 Logic Cone 12110 (labeled DATA1 in the drawingfigure) is coupled to the D1 input of scan flip-flop 12112 on Layer 1and the D0 input of scan flip-flop 12122 on Layer 2. Similarly, theoutput of Layer 2 Logic Cone 12120 (labeled DATA2 in the drawing figure)is coupled to the D1 input of scan flip-flop 12122 on Layer 2 and the D0input of scan flip-flop 12112 on Layer 1. Each of the scan flip-flops12112 and 12122 has its own LAYER_SEL signal (not shown in FIG. 121A)that selects between its D0 and D1 inputs in a manner similar to thatillustrated in FIG. 120.

XOR gate 12114 has a first input coupled to DATA1, a second inputcoupled to DATA2, and an output coupled to signal ERROR1. Similarly, XORgate 12124 has a first input coupled to DATA2, a second input coupled toDATA1, and an output coupled to signal ERROR2. If the logic valuespresent on the signals on DATA1 and DATA2 are not equal, ERROR1 andERROR2 will equal logic-1 signifying there is a logic error present. Ifthe signals on DATA1 and DATA2 are equal, ERROR1 and ERROR2 will equallogic-0 signifying there is no logic error present. Persons of ordinaryskill in art will appreciate that the underlying assumption here is thatonly one of the Logic Cones 12110 and 12120 will be bad simultaneously.Since both Layer 1 and Layer 2 have already been factory tested,verified and, in some embodiments, repaired, the statistical likelihoodof both logic cones developing a failure in the field is extremelyunlikely even without any factor repair, thus validating the assumption.

In 3DIC 12100, the testing may be done in a number of different ways asa matter of design choice. For example, the clock could be stoppedoccasionally and the status of the ERROR1 and ERROR2 signals monitoredin a spot check manner during a system maintenance period.Alternatively, operation can be halted and scan vectors run with acomparison done on every vector. In some embodiments, a BIST testingscheme using Linear Feedback Shift Registers to generate pseudo-randomvectors for Cyclic Redundancy Checking may be employed. These methodsall involve stopping system operation and entering a test mode. Othermethods of monitoring possible error conditions in real time will bediscussed below.

In order to effect a repair in 3D IC 12100, two determinations aretypically made: (1) the location of the logic cone with the error, and(2) which of the two corresponding logic cones is operating correctly atthat location. Thus a method of monitoring the ERROR1 and ERROR2 signalsand a method of controlling the LAYER_SEL signals of scan flip-flops12112 and 12122 are may be needed, though there are other approaches. Ina practical embodiment, a method of reading and writing the state of theLAYER_SEL signal may be needed for factory testing to verify that Layer1 and Layer 2 are both operating correctly.

Typically, the LAYER_SEL signal for each scan flip-flop will be held ina programmable element like, for example, a volatile memory circuit likea latch storing one bit of binary data (not shown in FIG. 121A). In someembodiments, the correct value of each programmable element or latch maybe determined at system power up, at a system reset, or on demand as aroutine part of system maintenance. Alternatively, the correct value foreach programmable element or latch may be determined at an earlier pointin time and stored in a non-volatile medium like a flash memory or byprogramming antifuses internal to 3D IC 12100, or the values may bestored elsewhere in the system in which 3D IC 12100 is deployed. Inthose embodiments, the data stored in the non-volatile medium may beread from its storage location in some manner and written to theLAYER_SEL latches.

Various methods of monitoring ERROR1 and ERROR2 are possible. Forexample, a separate shift register chain on each Layer (not shown inFIG. 121A) could be employed to capture the ERROR1 and ERROR2 values,though this would carry a significant area penalty. Alternatively, theERROR1 and ERROR2 signals could be coupled to scan flip-flops 12112 and12122 respectively (not shown in FIG. 121A), captured in a test mode,and shifted out. This would carry less overhead per scan flip-flop, butwould still be expensive.

The cost of monitoring the ERROR1 and ERROR2 signals can be reducedfurther if it is combined with the circuitry necessary to write and readthe latches storing the LAYER_SEL information. In some embodiments, forexample, the LAYER_SEL latch may be coupled to the corresponding scanflip-flop 12000 and have its value read and written through the scanchain. Alternatively, the logic cone, the scan flip-flop, the XOR gate,and the LAYER_SEL latch may all be addressed using the same addressingcircuitry.

Illustrated in FIG. 121B is circuitry for monitoring ERROR2 andcontrolling its associated LAYER_SEL latch by addressing in 3D IC 12100.Present in FIG. 121B is 3D IC 12100, a portion of the Layer 2 circuitryas discussed in FIG. 121A including scan flip-flop 12122 and XOR gate12124. A substantially identical circuit (not shown in FIG. 121B) willbe present on Layer 1 involving scan flip-flop 12112 and XOR gate 12114.

Also present in FIG. 121B is LAYER_SEL latch 12170 which is coupled toscan flip-flop 12122 through the LAYER_SEL signal. The value of the datastored in latch 12170 determines which logic cone is used by scanflip-flop 12122 in normal operation. Latch 12170 is coupled to COL_ADDRline 12174 (the column address line), ROW_ADDR line 12176 (the rowaddress line) and COL_BIT line 12178. These lines may be used to readand write the contents of latch 12170 in a manner similar to any SRAMcircuit known in the art. In some embodiments, a complementary COL_BITline (not shown in FIG. 121B) with inverted binary data may be present.In a logic design, whether implemented in full custom, semi-custom, gatearray or ASIC design or some other design methodology, the scanflip-flops will not line up neatly in rows and columns the way memorybit cells do in a memory block. In some embodiments, a tool may be usedto assign the scan flip-flops into virtual rows and columns foraddressing purposes. Then the various virtual row and column lines wouldbe routed like any other signals in the design.

The ERROR2 line 12172 may be read at the same address as latch 12170using the circuit including N-channel transistors 12182, 12184 and 12186and P-channel transistors 12190 and 12192. N-channel transistor 12182has a gate terminal coupled to ERROR2 line 12172, a source terminalcoupled to ground, and a drain terminal coupled to the source ofN-channel transistor 12184. N-channel transistor 12184 has a gateterminal coupled to COL_ADDR line 12174, a source terminal coupled toN-channel transistor 12182, and a drain terminal coupled to the sourceof N-channel transistor 12186. N-channel transistor 12186 has a gateterminal coupled to ROW_ADDR line 12176, a source terminal coupled tothe drain N-channel transistor 12184, and a drain terminal coupled tothe drain of P-channel transistor 12190 and the gate of P-channeltransistor 12192 through line 12188. P-channel transistor 12190 has agate terminal coupled to ground, a source terminal coupled to thepositive power supply, and a drain terminal coupled to line 12188.P-channel transistor 12192 has a gate terminal coupled to line 12188, asource terminal coupled to the positive power supply, and a drainterminal coupled to COL_BIT line 12178.

If the particular ERROR2 line 12172 in FIG. 121B is not addressed (i.e.,either COL_ADDR line 12174 equals the ground voltage level (logic-0) orROW_ADDR line 12176 equals the ground voltage supply voltage level(logic-0)), then the transistor stack including the three N-channeltransistors 12182, 12184 and 12186 will be non-conductive. The P-channeltransistor 12190 functions as a weak pull-up device pulling the voltagelevel on line 12188 to the positive power supply voltage (logic-1) whenthe N-channel transistor stack is non-conductive. This causes P-channeltransistor 12192 to be non-conductive presenting high impedance toCOL_BIT line 12178.

A weak pull-down (not shown in FIG. 121B) is coupled to COL_BIT line12178. If all the memory bit cells coupled to COL_BIT line 12178 presenthigh impedance, then the weak pull-down will pull the voltage level toground (logic-0).

If the particular ERROR2 line 12172 in FIG. 121B is addressed (i.e.,both COL_ADDR line 12174 and ROW_ADDR line 12176 are at the positivepower supply voltage level (logic-1)), then the transistor stackincluding the three N-channel transistors 12182, 12184 and 12186 will benon-conductive if ERROR2=logic-0 and conductive if ERROR2=logic-1. Thusthe logic value of ERROR2 may be propagated through P-channeltransistors 12190 and 12192 and onto the COL_BIT line 12178.

An advantage of the addressing scheme of FIG. 63B is that a broadcastready mode is available by addressing all of the rows and columnssimultaneously and monitoring all of the column bit lines 12178. If allthe column bit lines 12178 are logic-0, all of the ERROR2 signals arelogic-0 meaning there are no bad logic cones present on Layer 2. Sincefield correctable errors will be relatively rare, this can save a lot oftime locating errors relative to a scan flip-flop chain approach. If oneor more bit lines is logic-1, faulty logic cones will only be present onthose columns and the row addresses can be cycled quickly to find theirexact addresses. Another advantage of the scheme is that large groups orall of the LAYER_SEL latches can be initialized simultaneously to thedefault value of logic-1 quickly during a power up or reset condition.

At each location where a faulty logic cone is present, if any, thedefect is isolated to a particular layer so that the correctlyfunctioning logic cone may be selected by the corresponding scanflip-flop on both Layer 1 and Layer 2. If a large non-volatile memory ispresent in the 3D IC 12100 or in the external system, then automatictest pattern generated (ATPG) vectors may be used in a manner similar tothe factory repair embodiments. In this case, the scan itself is capableof identifying both the location and the correctly functioning layer.Unfortunately, this scan requires a large number of vectors and acorrespondingly large amount of available non-volatile memory which maynot be available in all embodiments.

Using some form of Built In Self-Test (BIST) leads to the advantage ofbeing self-contained inside 3D IC 12100 without needing the storage oflarge numbers of test vectors. Unfortunately, BIST tests tend to be ofthe “go” or “no go” variety. They identify the presence of an error, butare not particularly good at diagnosing either the location or thenature of the fault. Fortunately, there are ways to combine themonitoring of the error signals previously described with BISTtechniques and appropriate design methodology to quickly determine thecorrect values of the LAYER_SEL latches.

FIG. 122 illustrates an exemplary portion of the logic designimplemented in a 3D IC such as, for example, 11900 of FIG. 119 or 12100of FIG. 121A. The logic design is present on both Layer 1 and Layer 2with substantially identical gate-level implementations. Preferably, allof the flip-flops (not illustrated in FIG. 122) in the design areimplemented using scan flip-flops similar or identical in function toscan flip-flop 12000 of FIG. 120. Preferably, all of the scan flip-flopson each Layer have the sort of interconnections with the correspondingscan flip-flop on the other Layer as described in conjunction with FIG.121A. Preferably, each scan flip-flop will have an associated errorsignal generator (e.g., an XOR gate) for detecting the presence of afaulty logic cone, and a LAYER_SEL latch to control which logic cone isfed to the flip-flop in normal operating mode as described inconjunction with FIGS. 121A and 121B.

Present in FIG. 122 is an exemplary logic function block (LFB) 12200.Typically LFB 12200 has a plurality of inputs, an exemplary instancebeing indicated by reference number 12202, and a plurality of outputs,an exemplary instance being indicated by reference number 12204.Preferably LFB 12200 is designed in a hierarchical manner, meaning thatit typically has smaller logic function blocks such as 12210 and 12220instantiated within it. Circuits internal to LFBs 12210 and 12220 areconsidered to be at a “lower” level of the hierarchy than circuitspresent in the “top” level of LFB 12200 which are considered to be at a“higher” level in the hierarchy. LFB 12200 is exemplary only. Many otherconfigurations are possible. There may be more (or less) than two LFBsinstantiated internal to LFB 7500. There may also be individual logicgates and other circuits instantiated internal to LFB 12200 not shown inFIG. 122 to avoid overcomplicating the disclosure. LFBs 12210 and 12220may have internally instantiated even smaller blocks forming even lowerlevels in the hierarchy. Similarly, Logic Function Block 12200 mayitself be instantiated in another LFB at an even higher level of thehierarchy of the overall design.

Present in LFB 12200 is Linear Feedback Shift Register (LFSR) circuit12230 for generating pseudo-random input vectors for LFB 12200 in amanner well known in the art. In FIG. 122 one bit of LFSR 12230 isassociated with each of the inputs 12202 of LFB 12200. If an input 12202couples directly to a flip-flop (preferably a scan flip-flop similar to12000) then that scan flip-flop may be modified to have the additionalLFSR functionality to generate pseudo-random input vectors. If an input12202 couples directly to combinatorial logic, it will be intercepted intest mode and its value determined and replaced by a corresponding bitin LFSR 12230 during testing. Alternatively, the LFSR circuit 12230 willintercept all input signals during testing regardless of the type ofcircuitry it connects to internal to LFB 12200.

Thus during a BIST test, all the inputs of LFB 12200 may be exercisedwith pseudo-random input vectors generated by LSFR 12230. As is known inthe art, LSFR 12230 may be a single LSFR or a number of smaller LSFRs asa matter of design choice. LSFR 12230 is preferably implemented using aprimitive polynomial to generate a maximum length sequence ofpseudo-random vectors. LSFR 12230 needs to be seeded to a known value,so that the sequence of pseudo-random vectors is deterministic. Theseeding logic can be inexpensively implemented internal to the LSFR12230 flip-flops and initialized, for example, in response to a resetsignal.

Also present in LFB 12200 is Cyclic Redundancy Check (CRC) circuit 12232for generating a signature of the LFB 12200 outputs generated inresponse to the pseudo-random input vectors generated by LFSR 12230 in amanner well known in the art. In FIG. 122 one bit of CRC 12232 isassociated with each of the outputs 12204 of LFB 12200. If an output12204 couples directly to a flip-flop (preferably a scan flip-flopsimilar to 12000), then that scan flip-flop may be modified to have theadditional CRC functionality to generate the signature. If an output12204 couples directly to combinatorial logic, it will be monitored intest mode and its value coupled to a corresponding bit in CRC 12232.Alternatively, all the bits in CRC will passively monitor an outputregardless of the source of the signal internal to LFB 12200.

Thus during a BIST test, all the outputs of LFB 12200 may be analyzed todetermine the correctness of their responses to the stimuli provided bythe pseudo-random input vectors generated by LSFR 12230. As is known inthe art, CRC 12232 may be a single CRC or a number of smaller CRCs as amatter of design choice. As known in the art, a CRC circuit is a specialcase of an LSFR, with additional circuits present to merge the observeddata into the pseudo-random pattern sequence generated by the base LSFR.The CRC 12232 is preferably implemented using a primitive polynomial togenerate a maximum sequence of pseudo-random patterns. CRC 12232 needsto be seeded to a known value, so that the signature generated by thepseudo-random input vectors is deterministic. The seeding logic can beinexpensively implemented internal to the LSFR 12230 flip-flops andinitialized, for example, in response to a reset signal. Aftercompletion of the test, the value present in the CRC 12232 is comparedto the known value of the signature. If all the bits in CRC 12232 match,the signature is valid and the LFB 12200 is deemed to be functioningcorrectly. If one or more of the bits in CRC 12232 does not match, thesignature is invalid and the LFB 12200 is deemed to not be functioningcorrectly. The value of the expected signature can be inexpensivelyimplemented internal to the CRC 12232 flip-flops and compared internallyto CRC 12232 in response to an evaluate signal.

As shown in FIG. 122, LFB 12210 includes LFSR circuit 12212, CRC circuit12214, and logic function 12216. Since its input/output structure isanalogous to that of LFB 12200, it can be tested in a similar manneralbeit on a smaller scale. If 12200 is instantiated into a larger blockwith a similar input/output structure, 12200 may be tested as part ofthat larger block or tested separately as a matter of design choice. Itis not necessary that all blocks in the hierarchy have this input/outputstructure if it is deemed unnecessary to test them individually. Anexample of this is LFB 12220 instantiated inside LFB 12200 which doesnot have an LFSR circuit on the inputs and a CRC circuit on the outputsand which is tested along with the rest of LFB 12200.

Persons of ordinary skill in the art will appreciate that other BISTtest approaches are known in the art and that any of them may be used todetermine if LFB 12200 is functional or faulty.

In order to repair a 3D IC like 3D IC 12100 of FIG. 121A using the blockBIST approach, the part is put in a test mode and the DATA1 and DATA2signals are compared at each scan flip-flop 12000 on Layer 1 and Layer 2and the resulting ERROR1 and ERROR2 signals are monitored as describedin the above embodiments or possibly using some other method. Thelocation of the faulty logic cone is determined with regards to itslocation in the logic design hierarchy. For example, if the faulty logiccone were located inside LFB 12210 then the BIST routine for only thatblock would be run on both Layer 1 and Layer 2. The results of the twotests determine which of the blocks (and by implication which of thelogic cones) is functional and which is faulty. Then the LAYER_SELlatches for the corresponding scan flip-flops 12000 can be set so thateach receives the repair signal from the functional logic cone andignores the faulty signal. Thus the layer determination can be made fora modest cost in hardware in a shorter period of time without the needfor expensive ATPG testing.

FIG. 123 illustrates an alternative embodiment with the ability toperform field repair of individual logic cones. An exemplary 3D ICindicated generally by 12300 may include two layers labeled Layer 1 andLayer 2 and separated by a dashed line in the drawing figure. Layer 1and Layer 2 are bonded together to form 3D IC 12300 using methods knownin the art and interconnected using TSVs or some other interlayerinterconnect technology. Layer 1 may comprise Control Logic block 12310,scan flip-flops 12311 and 12312, multiplexers 12313 and 12314, and Logiccone 12315. Similarly, Layer 2 comprises Control Logic block 12320, scanflip-flops 12321 and 12322, multiplexers 12323 and 12324, and Logic cone12325.

In Layer 1, scan flip-flops 12311 and 12312 are coupled in series withControl Logic block 12310 to form a scan chain. Scan flip-flops 12311and 12312 can be ordinary scan flip-flops of a type known in the art.The Q outputs of scan flip-flops 12311 and 12312 are coupled to the D1data inputs of multiplexers 12313 and 12314 respectively. Representativelogic cone 12315 has a representative input coupled to the output ofmultiplexer 12313 and an output coupled to the D input of scan flip-flop12312.

In Layer 2, scan flip-flops 12321 and 12322 are coupled in series withControl Logic block 12320 to form a scan chain. Scan flip-flops 12321and 12322 can be ordinary scan flip-flops of a type known in the art.The Q outputs of scan flip-flops 12321 and 12322 are coupled to the D1data inputs of multiplexers 12323 and 12324 respectively. Representativelogic cone 12325 has a representative input coupled to the output ofmultiplexer 12323 and an output coupled to the D input of scan flip-flop12322.

The Q output of scan flip-flop 12311 is coupled to the D0 input ofmultiplexer 12323, the Q output of scan flip-flop 12321 is coupled tothe D0 input of multiplexer 12313, the Q output of scan flip-flop 12312is coupled to the D0 input of multiplexer 12324, and the Q output ofscan flip-flop 12322 is coupled to the D0 input of multiplexer 12314.Control Logic block 12310 is coupled to Control Logic block 12320 in amanner that allows coordination between testing functions betweenlayers. In some embodiments, the Control Logic blocks 12310 and 12320can test themselves or each other and, if one is faulty, the other cancontrol testing on both layers. These interlayer couplings may berealized by TSVs or by some other interlayer interconnect technology.

The logic functions performed on Layer 1 are substantially identical tothe logic functions performed on Layer 2. The embodiment of 3D IC 12300in FIG. 123 is similar to the embodiment of 3D IC 11900 shown in FIG.119, with the primary difference being that the multiplexers used toimplement the interlayer programmable or selectable cross couplings forlogic cone replacement are located immediately after the scan flip-flopsinstead of being immediately before them as in exemplary scan flip-flop12000 of FIG. 120 and in exemplary 3D IC 11900 of FIG. 119.

FIG. 124 illustrates an exemplary 3D IC indicated generally by 12400which is also constructed using this approach. Exemplary 3D IC 12400includes two Layers labeled Layer 1 and Layer 2 and separated by adashed line in the drawing figure. Layer 1 and Layer 2 are bondedtogether to form 3D IC 12400 and interconnected using TSVs or some otherinterlayer interconnect technology. Layer 1 comprises Layer 1 Logic Cone12410, scan flip-flop 12412, multiplexer 12414, and XOR gate 12416.Similarly, Layer 2 includes Layer 2 Logic Cone 12420, scan flip-flop12422, multiplexer 12424, and XOR gate 12426.

Layer 1 Logic Cone 12410 and Layer 2 Logic Cone 12420 implementsubstantially identical logic functions. In order to detect a faultylogic cone, the output of the logic cones 12410 and 12420 are capturedin scan flip-flops 12412 and 12422 respectively in a test mode. The Qoutputs of the scan flip-flops 12412 and 1262 are labeled Q1 and Q2respectively in FIG. 124. Q1 and Q2 are compared using the XOR gates12416 and 12426 to generate error signals ERROR1 and ERROR2respectively. Each of the multiplexers 12414 and 12424 has a selectinput coupled to a layer select latch (not shown in FIG. 124) preferablylocated in the same layer as the corresponding multiplexer withinrelatively close proximity to allow selectable or programmable couplingof Q1 and Q2 to either DATA1 or DATA2.

All the methods of evaluating ERROR1 and ERROR2 described in conjunctionwith the embodiments of FIGS. 121A, 121B and 122 may be employed toevaluate ERROR1 and ERROR2 in FIG. 124. Similarly, once ERROR1 andERROR2 are evaluated, the correct values may be applied to the layerselect latches for the multiplexers 12414 and 12424 to effect a logiccone replacement if necessary. In this embodiment, logic conereplacement also includes replacing the associated scan flip-flop.

FIG. 125A illustrates an exemplary embodiment with an even moreeconomical approach to realizing field repair. An exemplary 3D ICgenerally indicated by 12500 which includes two Layers labeled Layer 1and Layer 2 and separated by a dashed line in the drawing figure. Eachof Layer 1 and Layer 2 includes at least one Circuit Layer. Layer 1 andLayer 2 are bonded together using techniques known in the art to form 3DIC 12500 and interconnected with TSVs or other interlayer interconnecttechnology. Each Layer further includes an instance of Logic FunctionBlock 12510, each of which in turn comprises an instance of LogicFunction Block 12520. LFB 12520 includes LSFR circuits on its inputs(not shown in FIG. 125A) and CRC circuits on its outputs (not shown inFIG. 125A) in a manner analogous to that described with respect to LFB12200 in FIG. 122.

Each instance of LFB 12520 has a plurality of multiplexers 12522associated with its inputs and a plurality of multiplexers 12524associated with its outputs. These multiplexers may be used toprogrammably or selectively replace the entire instance of LFB 12520 oneither Layer 1 or Layer 2 with its counterpart on the other layer.

On power up, system reset, or on demand from control logic locatedinternal to 3D IC 12500 or elsewhere in the system where 3D IC 12500 isdeployed, the various blocks in the hierarchy can be tested. Any faultyblock at any level of the hierarchy with BIST capability may beprogrammably and selectively replaced by its corresponding instance onthe other Layer. Since this is determined at the block level, thisdecision can be made locally by the BIST control logic in each block(not shown in FIG. 125A), though some coordination may be required withhigher level blocks in the hierarchy with regards to which Layer theplurality of multiplexers 12522 sources the inputs to the functional LFB12520 in the case of multiple repairs in the same vicinity in the designhierarchy. Since both Layer 1 and Layer 2 preferably leave the factoryfully functional, or alternatively nearly fully functional, a simpleapproach is to designate one of the Layers, for example, Layer 1, as theprimary functional layer. Then the BIST controllers of each block cancoordinate locally and decide which block should have its inputs andoutputs coupled to Layer 1 through the Layer 1 multiplexers 12522 and12524.

Persons of ordinary skill in the art will appreciate that significantarea can be saved by employing this embodiment. For example, since LFBsare evaluated instead of individual logic cones, the interlayerselection multiplexers for each individual flip-flop like multiplexer12006 in FIG. 120 and multiplexer 12414 in FIG. 124 can be removed alongwith the LAYER_SEL latches 12170 of FIG. 121B since this function is nowhandled by the pluralities of multiplexers 12522 and 12524 in FIG. 125A,all of which may be controlled by one or more control signals inparallel. Similarly, the error signal generators (e.g., XOR gates 12114and 12124 in FIGS. 121A and 12416 and 7826 in FIG. 124) and anycircuitry needed to read them (e.g., coupling them to the scanflip-flops) or the addressing circuitry described in conjunction withFIG. 121B may also be removed, since in this embodiment entire LogicFunction Blocks, rather than individual Logic Cones, are being replaced.

Even the scan chains may be removed in some embodiments, though this isa matter of design choice. In embodiments where the scan chains areremoved, factory testing and repair would also have to rely on the blockBIST circuits. When a bad block is detected, an entire new block wouldneed to be crafted on the Repair Layer with e-Beam. Typically this takesmore time than crafting a replacement logic cone due to the greaternumber of patterns to shape, and the area savings may need to becompared to the test time losses to determine the economically superiordecision.

Removing the scan chains also entails a risk in the early debug andprototyping stage of the design, since BIST circuitry is not very goodfor diagnosing the nature of problems. If there is a problem in thedesign itself, the absence of scan testing will make it harder to findand fix the problem, and the cost in terms of lost time to market can bevery high and hard to quantify. Prudence might suggest leaving the scanchains in for reasons unrelated to the field repair aspects of thepresent invention.

Another advantage to embodiments using the block BIST approach isdescribed in conjunction with FIG. 125B. One disadvantage to some of theearlier embodiments is that the majority of circuitry on both Layer 1and Layer 2 is active during normal operation. Thus power can besubstantially reduced relative to earlier embodiments by operating onlyone instance of a block on one of the layers whenever possible.

Present in FIG. 125B are 3D IC 12500, Layer 1 and Layer 2, and twoinstances each of LFBs 12510 and 12520, and pluralities of multiplexers12522 and 12524 previously discussed. Also present in each Layer in FIG.125B is a power select multiplexer 12530 associated with that layer'sversion of LFB 12520. Each power select multiplexer 12530 has an outputcoupled to the power terminal of its associated LFB 12520, a firstselect input coupled to the positive power supply (labeled VCC in thefigure), and a second input coupled to the ground potential power supply(labeled GND in the figure). Each power select multiplexer 12530 has aselect input (not shown in FIG. 125B) coupled to control logic (also notshown in FIG. 125B), typically present in duplicate on Layer 1 and Layer2 though it may be located elsewhere internal to 3D IC 12500 or possiblyelsewhere in the system where 3D IC 12500 is deployed.

Persons of ordinary skill in the art will appreciate that there are manyways to programmably or selectively power down a block inside anintegrated circuit known in the art and that the use of powermultiplexer 12530 in the embodiment of FIG. 125B is exemplary only. Anymethod of powering down LFB 12520 is within the scope of the presentinvention. For example, a power switch could be used for both VCC andGND. Alternatively, the power switch for GND could be omitted and thepower supply node allowed to “float” down to ground when VCC isdecoupled from LFB 12530. In some embodiments, VCC may be controlled bya transistor, like either a source follower or an emitter follower whichis itself controlled by a voltage regulator, and VCC may be removed bydisabling or switching off the transistor in some way. Many otheralternatives are possible.

In some embodiments, control logic (not shown in FIG. 125B) uses theBIST circuits present in each block to stitch together a single copy ofthe design (using each block's plurality of input and outputmultiplexers which function similarly to pluralities of multiplexers12522 and 12524 associated with LFB 12520) including functional copiesof all the LFBs. When this mapping is complete, all of the faulty LFBsand the unused functional LFBs are powered off using their associatedpower select multiplexers (similar to power select multiplexer 12530).Thus the power consumption can be reduced to the level that a singlecopy of the design would require using standard two dimensionalintegrated circuit technology.

Alternatively, if a layer, for example, Layer 1 is designated as theprimary layer, then the BIST controllers in each block can independentlydetermine which version of the block is to be used. Then the settings ofthe pluralities of multiplexers 12522 and 12524 are set to couple theused block to Layer 1 and the settings of multiplexers 12530 can be setto power down the unused block. Typically, this should reduce the powerconsumption by half relative to embodiments where power selectmultiplexers 12530 or equivalent are not implemented.

There are test techniques known in the art that are a compromise betweenthe detailed diagnostic capabilities of scan testing with the simplicityof BIST testing. In embodiments employing such schemes, each BIST block(smaller than a typical LFB, but typically including a few tens to a fewhundreds of logic cones) stores a small number of initial states inparticular scan flip-flops while most of the scan flip-flops can use adefault value. CAD tools may be used to analyze the design's net-list toidentify the necessary scan flip-flops to allow efficient testing.

During test mode, the BIST controller shifts in the initial values andthen starts the clocking the design. The BIST controller has a signatureregister which might be a CRC or some other circuit which monitors bitsinternal to the block being tested. After a predetermined number ofclock cycles, the BIST controller stops clocking the design, shifts outthe data stored in the scan flip-flops while adding their contents tothe block signature, and compares the signature to a small number ofstored signatures (one for each of the stored initial states.

This approach has the advantage of not needing a large number of storedscan vectors and the “go” or “no go” simplicity of BIST testing. Thetest block is less fine than identifying a single faulty logic cone, butmuch coarser than a large Logic Function Block. In general, the finerthe test granularity (i.e., the smaller the size of the circuitry beingsubstituted for faulty circuitry) the less chance of a delayed faultshowing up in the same test block on both Layer 1 and Layer 2. Once thefunctional status of the BIST block has been determined, the appropriatevalues are written to the latches controlling the interlayermultiplexers to replace a faulty BIST block on one if the layers, ifnecessary. In some embodiments, faulty and unused BIST blocks may bepowered down to conserve power.

While discussions of the various exemplary embodiments described so farconcern themselves with finding and repairing defective logic cones orlogic function blocks in a static test mode, embodiments of the presentinvention can address failures due to noise or timing. For example, in3D IC 11900 of FIG. 119 and in 3D IC 12300 of FIG. 123 the scan chainscan be used to perform at-speed testing in a manner known in the art.One approach involves shifting a vector in through the scan chains,applying two or more at-speed clock pulses, and then shifting out theresults through the scan chain. This will catch any logic cones that arefunctionally correct at low speed testing but are operating too slowlyto function in the circuit at full clock speed. While this approach willallow field repair of slow logic cones, it may need the time,intelligence and memory capacity necessary to store, run, and evaluatescan vectors.

Another approach is to use block BIST testing at power up, reset, oron-demand to over-clock each block at ever increasing frequencies untilone fails, determine which layer version of the block is operatingfaster, and then substitute the faster block for the slower one at eachinstance in the design. This approach has the more modest time,intelligence and memory requirements generally associated with blockBIST testing, but it still needs placing of the 3D IC in a test mode.

FIG. 126 illustrates an embodiment where errors due to slow logic conescan be monitored in real time while the circuit is in normal operatingmode. An exemplary 3D IC generally indicated at 12600 includes twoLayers labeled Layer 1 and Layer 2 that are separated by a dashed linein the drawing figure. The Layers each include one or more CircuitLayers and are bonded together to form 3D IC 12600. The layers areelectrically coupled together using TSVs or some other interlayerinterconnect technology.

FIG. 126 focuses on the operation of circuitry coupled to the output ofa single Layer 2 Logic Cone 12620, though substantially identicalcircuitry is also present on Layer 1 (not shown in FIG. 126). Alsopresent in FIG. 126 is scan flip-flop 12622 with its D input coupled tothe output of Layer 2 Logic Cone 12620 and its Q output coupled to theD1 input of multiplexer 12624 through interlayer line 12612 labeled Q2in the figure. Multiplexer 12624 has an output DATA2 coupled to a logiccone (not shown in FIG. 126) and a D0 input coupled the Q1 output of theLayer 1 flip-flop corresponding to flip-flop 12622 (not shown in thefigure) through interlayer line 12610.

XOR gate 12626 has a first input coupled to Q1, a second input coupledto Q2, and an output coupled to a first input of AND gate 12646. ANDgate 12646 also has a second input coupled to TEST_EN line 12648 and anoutput coupled to the Set input of RS flip-flop3828. RS flip-flop alsohas a Reset input coupled to Layer 2 Reset line 12630 and an outputcoupled to a first input of OR gate 12632 and the gate of N-channeltransistor 12638. OR gate 12632 also has a second input coupled to Layer20R-chain Input line 12634 and an output coupled to Layer 20R-chainOutput line 12636.

Layer 2 control logic (not shown in FIG. 126) controls the operation ofXOR gate 12626, AND gate 12646, RS flip-flop 12628, and OR gate 12636.The TEST_EN line 12648 is used to disable the testing process withregards to Q1 and Q2. This is desirable in cases where, for example, afunctional error has already been repaired and differences between Q1and Q2 are routinely expected and would interfere with the backgroundtesting process looking for marginal timing errors.

Layer 2 Reset line 12630 is used to reset the internal state of RSflip-flop 12628 to logic-0 along with all the other RS flip-flopsassociated with other logic cones on Layer 2. OR gate 12632 is coupledtogether with all of the other OR-gates associated with other logiccones on Layer 2 to form a large Layer 2 distributed OR function coupledto all of the Layer 2 RS flip-flops like 12628 in FIG. 126. If all ofthe RS flip-flops are reset to logic-0, then the output of thedistributed OR function will be logic-0. If a difference in logic stateoccurs between the flip-flops generating the Q1 and Q2 signals, XOR gate12626 will present a logic-1 through AND gate 12646 (if TEST_EN=logic-1)to the Set input of RS flip-flop 12628 causing it to change state andpresent a logic-1 to the first input of OR gate 12632, which in turnwill produce a logic-1 at the output of the Layer 2 distributed ORfunction (not shown in FIG. 126) notifying the control logic (not shownin the figure) that an error has occurred.

The control logic can then use the stack of N-channel transistors 12638,12640 and 12642 to determine the location of the logic cone producingthe error. Transistor 12638 has a gate terminal coupled to the Q outputof RS flip-flop 12628, a source terminal coupled to ground, and a drainterminal coupled to the source of transistor 12640. Transistor 12640 hasa gate terminal coupled to the row address line ROW_ADDR line, a sourceterminal coupled to the drain of transistor 12638, and a drain terminalcoupled to the source of transistor 12642. Transistor 12642 has a gateterminal coupled to the column address line COL_ADDR line, a sourceterminal coupled to the drain of transistor 12640, and a drain terminalcoupled to the sense line SENSE.

The row and column addresses are virtual addresses, since in a logicdesign the locations of the flip-flops will not be neatly arranged inrows and columns. In some embodiments a Computer Aided Design (CAD) toolis used to modify the net-list to correctly address each logic cone andthen the ROW_ADDR and COL_ADDR signals are routed like any other signalin the design.

This produces an efficient way for the control logic to cycle throughthe virtual address space. If COL_ADDR=ROW_ADDR=logic-1 and the state ofRS flip-flop is logic-1, then the transistor stack will pullSENSE=logic-0. Thus a logic-1 will only occur at a virtual addresslocation where the RS flip-flop has captured an error. Once an error hasbeen detected, RS flip-flop 12628 can be reset to logic-0 with the Layer2 Reset line 12630 where it will be able to detect another error in thefuture.

The control logic can be designed to handle an error in any of a numberof ways. For example, errors can be logged and if a logic error occursrepeatedly for the same logic cone location, then a test mode can beentered to determine if a repair is necessary at that location. This isa good approach to handle intermittent errors resulting from marginallogic cones that only occasionally fail, for example, due to noise, andmay be tested as functional in normal testing. Alternatively, action canbe taken upon receipt of the first error notification as a matter ofdesign choice.

As discussed earlier in conjunction with FIG. 27, using Triple ModularRedundancy (TMR) at the logic cone level can also function as aneffective field repair method, though it really creates a high level ofredundancy that masks rather than repairs errors due to delayed failuremechanisms or marginally slow logic cones. If factory repair is used tomake sure all the equivalent logic cones on each layer test functionalbefore the 3D IC is shipped from the factory, the level of redundancy iseven higher. The cost of having three layers versus having two layers,with or without a repair layer must be factored into determining thebest embodiment for any application.

An alternative TMR approach is shown in exemplary 3D IC 12700 in FIG.127. Present in FIG. 127 are substantially identical Layers labeledLayer 1, Layer 2 and Layer 3 separated by dashed lines in the figure.Layer 1, Layer 2 and Layer 3 may each include one or more circuit layersand are bonded together to form 3D IC 12700 using techniques known inthe art. Layer 1 comprises Layer 1 Logic Cone 12710, flip-flop 12714,and majority-of-three (MAJ3) gate 12716. Layer 2 may include Layer 2Logic Cone 12720, flip-flop 12724, and MAJ3 gate 12726. Layer 3 mayinclude Layer 3 Logic Cone 12730, flip-flop 12734, and MAJ3 gate 12736.

The logic cones 12710, 12720 and 12730 all perform a substantiallyidentical logic function. The flip-flops 12714, 12724 and 12734 arepreferably scan flip-flops. If a Repair Layer is present (not shown inFIG. 127), then the flip-flop 2502 of FIG. 25 may be used to implementrepair of a defective logic cone before 3D IC 12700 is shipped from thefactory. The MAJ3 gates 12716, 12726 and 12736 compare the outputs fromthe three flip-flops 12714, 12724 and 12734 and output a logic valueconsistent with the majority of the inputs: specifically if two or threeof the three inputs equal logic-0, then the MAJ3 gate will outputlogic-0; and if two or three of the three inputs equal logic-1, then theMAJ3 gate will output logic-1. Thus if one of the three logic cones orone of the three flip-flops is defective, the correct logic value willbe present at the output of all three MAJ3 gates.

One advantage of the embodiment of FIG. 127 is that Layer 1, Layer 2 orLayer 3 can all be fabricated using all or nearly all of the same masks.Another advantage is that MAJ3 gates 12716, 12726 and 12736 alsoeffectively function as a Single Event Upset (SEU) filter for highreliability or radiation tolerant applications as described in Rezguicited above.

Another TMR approach is shown in exemplary 3D IC 12800 in FIG. 128. Inthis embodiment, the MAJ3 gates are placed between the logic cones andtheir respective flip-flops. Present in FIG. 128 are substantiallyidentical Layers labeled Layer 1, Layer 2 and Layer 3 separated bydashed lines in the figure. Layer 1, Layer 2 and Layer 3 may eachinclude one or more circuit layers and are bonded together to form 3D IC12800 using techniques known in the art. Layer 1 comprises Layer 1 LogicCone 12810, flip-flop 12814, and majority-of-three (MAJ3) gate 12812.Layer 2 may include Layer 2 Logic Cone 12820, flip-flop 12824, and MAJ3gate 12822. Layer 3 may include Layer 3 Logic Cone 12830, flip-flop12834, and MAJ3 gate 12832.

The logic cones 12810, 12820 and 12830 all perform a substantiallyidentical logic function. The flip-flops 12814, 12824 and 12834 arepreferably scan flip-flops. If a Repair Layer is present (not shown inFIG. 128), then the flip-flop 2502 of FIG. 25 may be used to implementrepair of a defective logic cone before 3D IC 12800 is shipped from thefactory. The MAJ3 gates 12812, 12822 and 12832 compare the outputs fromthe three logic cones 12810, 12820 and 12830 and output a logic valueconsistent with the majority of the inputs. Thus if one of the threelogic cones is defective, the correct logic value will be present at theoutput of all three MAJ3 gates.

One advantage of the embodiment of FIG. 128 is that Layer 1, Layer 2 orLayer 3 can all be fabricated using all or nearly all of the same masks.Another advantage is that MAJ3 gates 12712, 12722 and 12732 alsoeffectively function as a Single Event Transient (SET) filter for highreliability or radiation tolerant applications as described in Rezguicited above.

Another TMR embodiment is shown in exemplary 3D IC 12900 in FIG. 129. Inthis embodiment, the MAJ3 gates are placed between the logic cones andtheir respective flip-flops. Present in FIG. 129 are substantiallyidentical Layers labeled Layer 1, Layer 2 and Layer 3 separated bydashed lines in the figure. Layer 1, Layer 2 and Layer 3 may eachinclude one or more circuit layers and are bonded together to form 3D IC12900 using techniques known in the art. Layer 1 comprises Layer 1 LogicCone 12910, flip-flop 12914, and majority-of-three (MAJ3) gates 12912and 12916. Layer 2 may include Layer 2 Logic Cone 12920, flip-flop12924, and MAJ3 gates 12922 and 12926. Layer 3 may include Layer 3 LogicCone 12930, flip-flop 12934, and MAJ3 gates 12932 and 12936.

The logic cones 12910, 12920 and 12930 all perform a substantiallyidentical logic function. The flip-flops 12914, 12924 and 12934 arepreferably scan flip-flops. If a Repair Layer is present (not shown inFIG. 129), then the flip-flop 2502 of FIG. 25 may be used to implementrepair of a defective logic cone before 3D IC 12900 is shipped from thefactory. The MAJ3 gates 12912, 12922 and 12932 compare the outputs fromthe three logic cones 12910, 12920 and 12930 and output a logic valueconsistent with the majority of the inputs. Similarly, the MAJ3 gates12916, 12926 and 12936 compare the outputs from the three flip-flops12914, 12924 and 12934 and output a logic value consistent with themajority of the inputs. Thus if one of the three logic cones or one ofthe three flip-flops is defective, the correct logic value will bepresent at the output of all six of the MAJ3 gates.

One advantage of the embodiment of FIG. 129 is that Layer 1, Layer 2 orLayer 3 can all be fabricated using all or nearly all of the same masks.Another advantage is that MAJ3 gates 12712, 12722 and 12732 alsoeffectively function as a Single Event Transient (SET) filter while MAJ3gates 12716, 12726 and 12736 also effectively function as a Single EventUpset (SEU) filter for high reliability or radiation tolerantapplications as described in Rezgui cited above.

Some embodiments of the present invention can be applied to a largevariety of commercial as well as high-reliability aerospace and militaryapplications. The ability to fix defects in the factory with RepairLayers combined with the ability to automatically fix delayed defects(by masking them with three layer TMR embodiments or replacing faultycircuits with two layer replacement embodiments) allows the creation ofmuch larger and more complex three dimensional systems than is possiblewith conventional two dimensional integrated circuit (IC) technology.These various aspects of the present invention can be traded off againstthe cost requirements of the target application.

In order to reduce the cost of a 3D IC according to some embodiments ofthe present invention, it is desirable to use the same set of masks tomanufacture each Layer. This can be done by creating an identicalstructure of vias in an appropriate pattern on each layer and thenoffsetting it by a desired amount when aligning Layer 1 and Layer 2.

FIG. 130A illustrates a via pattern 13000 which is constructed on Layer1 of 3D ICs like 11900, 12100, 12200, 12300, 12400, 12500 and 12600previously discussed. At a minimum the metal overlap pad at each vialocation 13002, 13004, 13006 and 13008 may be present on the top andbottom metal layers of Layer 1. Via pattern 13000 occurs in proximity toeach repair or replacement multiplexer on Layer 1 where via metaloverlap pads 13002 and 13004 (labeled L1/D0 for Layer 1 input D0 in thefigure) are coupled to the D0 multiplexer input at that location, andvia metal overlap pads 13006 and 13008 (labeled L1/D1 for Layer 1 inputD1 in the figure) are coupled to the D1 multiplexer input.

Similarly, FIG. 130B illustrates a substantially identical via pattern13010 which is constructed on Layer 2 of 3D ICs like 11900, 12100,12200, 12300, 12400, 12500 and 12600 previously discussed. At a minimumthe metal overlap pad at each via location 13012, 13014, 13016 and 13018may be present on the top and bottom metal layers of Layer 2. Viapattern 13010 occurs in proximity to each repair or replacementmultiplexer on Layer 2 where via metal overlap pads 13012 and 13014(labeled L2/D0 for Layer 2 input D0 in the figure) are coupled to the D0multiplexer input at that location, and via metal overlap pads 13016 and13018 (labeled L2/D1 for Layer 2 input D1 in the figure) are coupled tothe D1 multiplexer input.

FIG. 130C illustrates a top view where via patterns 13000 and 13010 arealigned offset by one interlayer interconnection pitch. The interlayerinterconnects may be TSVs or some other interlayer interconnecttechnology. Present in FIG. 130C are via metal overlap pads 13002,13004, 13006, 13008, 13012, 13014, 13016 and 13018 previously discussed.In FIG. 130C Layer 2 is offset by one interlayer connection pitch to theright relative to Layer 1. This offset causes via metal overlap pads13004 and 13018 to physically overlap with each other. Similarly, thisoffset causes via metal overlap pads 13006 and 13012 to physicallyoverlap with each other. If Through Silicon Vias or other interlayervertical coupling points are placed at these two overlap locations(using a single mask) then multiplexer input D1 of Layer 2 is coupled tomultiplexer input D0 of Layer 1 and multiplexer input D0 of Layer 2 iscoupled to multiplexer input D1 of Layer 1. This is precisely theinterlayer connection topology necessary to realize the repair orreplacement of logic cones and functional blocks in, for example, theembodiments described with respect to FIGS. 121A and 123.

FIG. 130D illustrates a side view of a structure employing the techniquedescribed in conjunction with FIGS. 130A, 130B and 130C. Present in FIG.130D is an exemplary 3D IC generally indicated by 13020 comprising twoinstances of Layer 13030 stacked together with the top instance labeledLayer 2 and the bottom instance labeled Layer 1 in the figure. Eachinstance of Layer 13020 may include an exemplary transistor 13031, anexemplary contact 13032, exemplary metal 1 13033, exemplary via 1 13034,exemplary metal 2 13035, exemplary via 2 13036, and exemplary metal 313037. The dashed oval labeled 13000 indicates the part of the Layer 1corresponding to via pattern 13000 in FIGS. 130A and 130C. Similarly,the dashed oval labeled 13010 indicates the part of the Layer 2corresponding to via pattern 13010 in FIGS. 130B and 130C. An interlayervia such as TSV 13040 in this example is shown coupling the signal D1 ofLayer 2 to the signal D0 of Layer 1. A second interlayer via (not shownsince it is out of the plane of FIG. 130D) couples the signal D01 ofLayer 2 to the signal D1 of Layer 1. As can be seen in FIG. 130D, whileLayer 1 is identical to Layer 2, Layer 2 is offset by one interlayer viapitch allowing the TSVs to correctly align to each layer while onlyrequiring a single interlayer via mask to make the correct interlayerconnections.

As previously discussed, in some embodiments of the present invention itis desirable for the control logic on each Layer of a 3D IC to knowwhich layer it is. It is also desirable to use all of the same masks foreach Layers. In an embodiment using the one interlayer via pitch offsetbetween layers to correctly couple the functional and repairconnections, a different via pattern can be placed in proximity to thecontrol logic to exploit the interlayer offset and uniquely identifyeach of the layers to its control logic.

FIG. 131A illustrates a via pattern 13100 which is constructed on Layer1 of 3D ICs like 11900, 12100, 12200, 12300, 12400, 12500 and 12600previously discussed. At a minimum the metal overlap pad at each vialocation 13102, 13104, and 13106 may be present on the top and bottommetal layers of Layer 1. Via pattern 13100 occurs in proximity tocontrol logic on Layer 1. Via metal overlap pad 13102 is coupled toground (labeled L1/G in the figure for Layer 1 Ground). Via metaloverlap pad 13104 is coupled to a signal named ID (labeled L1/ID in thefigure for Layer 1 ID). Via metal overlap pad 13106 is coupled to thepower supply voltage (labeled L1/V in the figure for Layer 1 VCC).

FIG. 131B illustrates a via pattern 13110 which is constructed on Layer1 of 3D ICs like 11900, 12100, 12200, 12300, 12400, 12500 and 12600previously discussed. At a minimum the metal overlap pad at each vialocation 13112, 13114, and 13116 may be present on the top and bottommetal layers of Layer 2. Via pattern 13110 occurs in proximity tocontrol logic on Layer 2. Via metal overlap pad 13112 is coupled toground (labeled L2/G in the figure for Layer 2 Ground). Via metaloverlap pad 13114 is coupled to a signal named ID (labeled L2/ID in thefigure for Layer 2 ID). Via metal overlap pad 13116 is coupled to thepower supply voltage (labeled L2/V in the figure for Layer 2 VCC).

FIG. 131C illustrates a top view where via patterns 13100 and 13110 arealigned offset by one interlayer interconnection pitch. The interlayerinterconnects may be TSVs or some other interlayer interconnecttechnology. Present in FIG. 130C are via metal overlap pads 13102,13104, 13106, 13112, 13114, and 13016 previously discussed. In FIG. 130CLayer 2 is offset by one interlayer connection pitch to the rightrelative to Layer 1. This offset causes via metal overlap pads 13104 and13112 to physically overlap with each other. Similarly, this offsetcauses via metal overlap pads 13106 and 13114 to physically overlap witheach other. If Through Silicon Vias or other interlayer verticalcoupling points are placed at these two overlap locations (using asingle mask) then the Layer 1 ID signal is coupled to ground and theLayer 2 ID signal is coupled to VCC. This configuration allows thecontrol logic in Layer 1 and Layer 2 to uniquely know their verticalposition in the stack.

Persons of ordinary skill in the art will appreciate that the metalconnections between Layer 1 and Layer 2 will typically be much largerincluding larger pads and numerous TSVs or other interlayerinterconnections. This increased size makes alignment of the powersupply nodes easy and ensures that L1/V and L2/V will both be at thepositive power supply potential and that L1/G and L2/G will both be atground potential.

Several embodiments of the present invention utilize Triple ModularRedundancy (TMR) distributed over three Layers. In such embodiments itmay be desirable to use the same masks for all three Layers.

FIG. 132A illustrates a via metal overlap pattern 13200 including a 3×3array of TSVs (or other interlayer coupling technology). The TMRinterlayer connections occur in the proximity of a majority-of-three(MAJ3) gate typically fanning in or out from either a flip-flop orfunctional block. Thus at each location on each of the three layers wehave the function f(X0, X1, X2)=MAJ3(X0, X1, X2) being implemented whereX0, X1 and X2 are the three inputs to the MAJ3 gate. For purposes ofthis discussion, the X0 input is always coupled to the version of thesignal generated on the same layer as the MAJ3 gate and the X1 and X2inputs come from the other two layers.

In via pattern 13200, via metal overlap pads 13202, 13212 and 13216 arecoupled to the X0 input of the MAJ3 gate on that layer, via metaloverlap pads 13204, 13208 and 13218 are coupled to the X1 input of theMAJ3 gate on that layer, and via metal overlap pads 13206, 13210 and13214 are coupled to the X2 input of the MAJ3 gate on that layer.

FIG. 132B illustrates an exemplary 3D IC generally indicated by 9220having three Layers labeled Layer 1, Layer 2 and Layer 3 from bottom totop. Each layer may include an instance of via pattern 13200 in theproximity of each MAJ3 gate used to implement a TMR related interlayercoupling. Layer 2 is offset one interlayer via pitch to the rightrelative to Layer 1 while Layer 3 is offset one interlayer via pitch tothe right relative to Layer 2. The illustration in FIG. 132B is anabstraction. While it correctly shows the two interlayer via pitchoffsets in the horizontal direction, a person of ordinary skill in theart will realize that each row of via metal overlap pads in eachinstance of 13200 is horizontally aligned with the same row in the otherinstances.

Thus there are three locations where a via metal overlap pad is alignedon all three layers. FIG. 132B shows three interlayer vias 13230, 13240and 13250 placed in those locations coupling Layer 1 to Layer 2 andthree more interlayer vias 13232, 13242 and 13252 placed in thoselocations coupling Layer 2 to Layer 3. The same interlayer via mask maybe used for both interlayer via fabrication steps.

Thus the interlayer vias 13230 and 13232 are vertically aligned andcouple together the Layer 1 X2 MAJ3 gate input, the Layer 2 X0 MAJ3 gateinput, and the Layer 3 X1 MAJ3 gate input. Similarly, the interlayervias 13240 and 13242 are vertically aligned and couple together theLayer 1 X1 MAJ3 gate input, the Layer 2 X2 MAJ3 gate input, and theLayer 3 X0 MAJ3 gate input. Finally, the interlayer vias 13250 and 13252are vertically aligned and couple together the Layer 1 X0 MAJ3 gateinput, the Layer 2 X1 MAJ3 gate input, and the Layer 3 X2 MAJ3 gateinput. Since the X0 input of the MAJ3 gate in each layer is driven fromthat layer, each driver is coupled to a different MAJ3 gate input oneach layer preventing drivers from being shorted together and the eachMAJ3 gate on each layer receives inputs from each of the three driverson the three Layers.

Some embodiments of the present invention can be applied to a largevariety of commercial as well as high-reliability aerospace and militaryapplications. The ability to fix defects in the factory with RepairLayers combined with the ability to automatically fix delayed defects(by masking them with three layer TMR embodiments or replacing faultycircuits with two layer replacement embodiments) allows the creation ofmuch larger and more complex three dimensional systems than is possiblewith conventional two dimensional integrated circuit (IC) technology.These various aspects of the present invention can be traded off againstthe cost requirements of the target application.

For example, a 3D IC targeted at inexpensive consumer products wherecost is dominant consideration might do factory repair to maximize yieldin the factory but not include any field repair circuitry to minimizecosts in products with short useful lifetimes. A 3D IC aimed at higherend consumer or lower end business products might use factory repaircombined with two layer field replacement. A 3D IC targeted atenterprise class computing devices which balance cost and reliabilitymight skip doing factory repair and use TMR for both acceptable yieldsas well as field repair. A 3D IC targeted at high reliability, military,aerospace, space, or radiation-tolerant applications might do factoryrepair to ensure that all three instances of every circuit are fullyfunctional and use TMR for field repair as well as SET and SEUfiltering. Battery operated devices for the military market might addcircuitry to allow the device to operate only one of the three TMRlayers to save battery life and include a radiation detection circuitwhich automatically switches into TMR mode when needed if the operatingenvironment changes. Many other combinations and tradeoffs are possiblewithin the scope of the invention.

It is worth noting that many of the principles of the present inventionare also applicable to conventional two dimensional integrated circuits(2D ICs). For example, an analogous of the two layer field repairembodiments could be built on a single layer with both versions of theduplicate circuitry on a single 2D IC employing the same crossconnections between the duplicate versions. A programmable technologylike, for example, fuses, antifuses, flash memory storage, etc., couldbe used to effect both factory repair and field repair. Similarly, ananalogous versions of some of the TMR embodiments are unique topologiesin 2D ICs as well as in 3D ICs which would also improve the yield orreliability of 2D IC systems if implemented on a single layer.

FIG. 13 is a flow-chart illustration for 3D logic partitioning. Thepartitioning of a logic design to two or more vertically connected diespresents a different challenge for a Place and Route—P&R—tool. A placeand route tool is a type of CAD software capable of operating onlibraries of logic cells (as well as libraries of other types of cells)as previously discussed. The common layout flow of prior art P & R toolsmay typically start with planning the placement followed by the routing.But the design of the logic of vertically connected dies may givepriority to the much-reduced frequency of connections between dies andmay create a need for a special design flow and CAD softwarespecifically to support the design flow. In fact, a 3D system mightmerit planning some of the routing first as presented in the flows ofFIG. 13.

The flow chart of FIG. 13 uses the following terms:

M—The number of TSVs available for logic;

N(n)—The number of nodes connected to net n;

S(n)—The median slack of net n;

MinCut—a known algorithm to partition logic design (net-list) to twopieces about equal in size with a minimum number of nets (MC) connectingthe pieces;

MC—number of nets connecting the two partitions;

K1, K2—Two parameters selected by the designer.

One idea of the proposed flow of FIG. 13 is to construct a list of netsin the logic design that connect more than K1 nodes and less than K2nodes. K1 and K2 are parameters that could be selected by the designerand could be modified in an iterative process. K1 should be high enoughso to limit the number of nets put into the list. The flow's objectiveis to assign the TSVs to the nets that have tight timingconstraints-critical nets. And also have many nodes whereby having theability to spread the placement on multiple die help to reduce theoverall physical length to meet the timing constraints. The number ofnets in the list should be close but smaller than the number of TSVs.Accordingly K1 should be set high enough to achieve this objective. K2is the upper boundary for nets with the number of nodes N(n) that wouldjustify special treatment.

Critical nets may be identified usually by using static timing analysisof the design to identify the critical paths and the available “slack”time on these paths, and pass the constraints for these paths to thefloor planning, layout, and routing tools so that the final design isnot degraded beyond the requirement.

Once the list is constructed it is priority-ordered according toincreasing slack, or the median slack, S(n), of the nets. Then, using apartitioning algorithm, such as, but not limited to, MinCut, the designmay be split into two parts, with the highest priority nets split aboutequally between the two parts. The objective is to give the nets thathave tight slack a better chance to be placed close enough to meet thetiming challenge. Those nets that have higher than K1 nodes tend to getspread over a larger area, and by spreading into three dimensions we geta better chance to meet the timing challenge.

The Flow of FIG. 13 suggests an iterative process of allocating the TSVsto those nets that have many nodes and are with the tightest timingchallenge, or smallest slack.

Clearly the same Flow could be adjusted to three-way partition or anyother number according to the number of dies the logic will be spreadon.

Constructing a 3D Configurable System comprising antifuse based logicalso provides features that may implement yield enhancement throughutilizing redundancies. This may be even more convenient in a 3Dstructure of embodiments of the present invention because the memoriesmay not be sprinkled between the logic but may rather be concentrated inthe memory die, which may be vertically connected to the logic die.Constructing redundancy in the memory, and the proper self-repair flow,may have a smaller effect on the logic and system performance.

The potential dicing streets of the continuous array of this presentinvention represent some loss of silicon area. The narrower the streetthe lower the loss is, and therefore, it may be advantageous to useadvanced dicing techniques that can create and work with narrow streets.

One such advanced dicing technique may be the use of lasers for dicingthe 3D IC wafers. Laser dicing techniques, including the use of waterjets to cool the substrate and remove debris, may be employed tominimize damage to the 3D IC structures and may also be utilized to cutsensitive layers in the 3D IC, and then a conventional saw finish may beused.

An additional advantage of the 3D Configurable System of variousembodiments of this present invention may be a reduction in testingcost. This is the result of building a unique system by using standard‘Lego®’ blocks. Testing standard blocks could reduce the cost of testingby using standard probe cards and standard test programs.

The disclosure presents two forms of 3D IC system, first by using TSVand second by using the method referred to herein as the ‘Attic’described in, for example, FIGS. 21 to 35 and 39 to 40. Those twomethods could even work together as a devices could have multiple layersof mono- or poly-crystalline silicon produced using layer transfer ordeposits and the techniques referred to herein as the ‘Foundation’ andthe ‘Attic’ and then connected together using TSV. The most significantdifference is that prior TSVs are associated with a relatively largemisalignment (approximately 1 micron) and limited connections (TSV) permm sq. of approximately 10,000 for a connected fully fabricated devicewhile the disclosed ‘smart-cut’-layer transferred techniques allow 3Dstructures with a very small misalignment (<10 nm) and high number ofconnections (vias) per mm sq. of approximately 100,000,000, since theyare produced in an integrated fabrication flow. An advantage of 3D usingTSV is the ability to test each device before integrating it and utilizethe Known Good Die (KGD) in the 3D stack or system. This is very helpfulto provide good yield and reasonable costs of the 3D Integrated System.

An additional alternative of the present invention is a method to allowredundancy so that the highly integrated 3D systems using the layertransfer technique could be produced with good yield. For the purpose ofillustrating this redundancy invention we will use the programmable tilearray presented in FIGS. 11A, 36-38.

FIG. 41 is a drawing illustration of a 3D IC system with redundancy. Itillustrates a 3D IC programmable system comprising: first programmablelayer 4100 of 3×3 tiles 4102, overlaid by second programmable layer 4110of 3×3 tiles 4112, overlaid by third programmable layer 4120 of 3×3tiles 4122. Between a tile and its neighbor tile in the layer there aremany programmable connections 4104. The programmable element 4106 couldbe antifuse, pass transistor controlled driver, floating gate flashtransistor, or similar electrically programmable element. Eachinter-tile connection 4104 has a branch out programmable connection 4105connected to inter-layer vertical connection 4140. The end product isdesigned so that at least one layer such as 4110 is left for redundancy.

When the end product programmable system is being programmed for the endapplication each tile will run its own Built-in Test using its own MCU.A tile that is detected to have a defect will be replaced by the tile inthe redundancy layer 4110. The replacement will be done by the tile thatis at the same location but in the redundancy layer and therefore itshould have an acceptable impact on the overall product functionalityand performance. For example, if tile (1,0,0) has a defect then tile(1,0,1) will be programmed to have exactly the same function and willreplace tile (1,0,0) by properly setting the inter tile programmableconnections. Therefore, if defective tile (1,0,0) was supposed to beconnected to tile (2,0,0) by connection 4104 with programmable element4106, then programmable element 4106 would be turned off andprogrammable elements 4116, 4117, 4107 will be turned on instead. Asimilar multilayer connection structure should be used for anyconnection in or out of a repeating tile. So if the tile has a defectthe redundant tile of the redundant layer would be programmed to thedefected tile functionality and the multilayer inter tile structurewould be activated to disconnect the faulty tile and connect theredundant tile. The inter layer vertical connection 4140 could be alsoused when tile (2,0,0) is defective to insert tile (2,0,1), of theredundant layer, instead. In such case (2,0,1) will be programmed tohave exactly the same function as tile (2,0,0), programmable element4108 will be turned off and programmable elements 4118, 4117, 4107 willbe turned on instead.

An additional embodiment of the present invention may be a modified TSV(Through Silicon Via) flow. This flow may be for wafer-to-wafer TSV andmay provide a technique whereby the thickness of the added wafer may bereduced to about 1 micrometer (micron). FIGS. 93 A to D illustrate sucha technique. The first wafer 9302 may be the base on top of which the‘hybrid’ 3D structure may be built. A second wafer 9304 may be bonded ontop of the first wafer 9302. The new top wafer may be face-down so thatthe circuits 9305 may be face-to-face with the first wafer 9302 circuits9303.

The bond may be oxide-to-oxide in some applications or copper-to-copperin other applications. In addition, the bond may be by a hybrid bondwherein some of the bonding surface may be oxide and some may be copper.

After bonding, the top wafer 9304 may be thinned down to about 60 micronin a conventional back-lap and CMP process. FIG. 93B illustrates the nowthinned wafer 9306 bonded to the first wafer 9302.

The next step may comprise a high accuracy measurement of the top wafer9306 thickness. Then, using a high power 1-4 MeV H+ implant, a cleaveplane 9310 may be defined in the top wafer 9306. The cleave plane 9310may be positioned approximately 1 micron above the bond surface asillustrated in FIG. 93C. This process may be performed with a specialhigh power implanter such as, for example, the implanter used by SiGenCorporation for their PV (PhotoVoltaic) application.

Having the accurate measure of the top wafer 9306 thickness and thehighly controlled implant process may enable cleaving most of the topwafer 9306 out thereby leaving a very thin layer 9312 of about 1 micron,bonded on top of the first wafer 9302 as illustrated in FIG. 93D.

An advantage of this process flow may be that an additional wafer withcircuits could now be placed and bonded on top of the bonded structure9322 in a similar manner. But first a connection layer may be built onthe back of 9312 to allow electrical connection to the bonded structure9322 circuits. Having the top layer thinned to a single micron level mayallow such electrical connection metal layers to be fully aligned to thetop wafer 9312 electrical circuits 9305 and may allows the vias throughthe back side of top layer 9312 to be relatively small, of about 100 nmin diameter.

The thinning of the top layer 9312 may enable the modified TSV to be atthe level of 100 nm vs. the 5 microns necessary for TSVs that need to gothrough 50 microns of silicon. Unfortunately the misalignment of thewafer-to-wafer bonding process may still be quite significant at about+/−0.5 micron. Accordingly, as described elsewhere in this document inrelation to FIG. 75, a landing pad of approximately 1×1 microns may beused on the top of the first wafer 9302 to connect with a small metalcontact on the face of the second wafer 9304 while usingcopper-to-copper bonding. This process may represent a connectiondensity of approximately 1 connection per 1 square micron.

It may be desirable to increase the connection density using a conceptas illustrated in FIG. 80 and the associated explanations. In themodified TSV case, it may be much more challenging to do so because thetwo wafers being bonded may be fully processed and once bonded, onlyvery limited access to the landing strips may be available. However, toconstruct a via, etching through all layers may be needed. FIG. 94illustrates a method and structures to address these issues.

FIG. 94A illustrates four metal landing strips 9402 exposed at the upperlayer of the first wafer 9302. The landing strips 9402 may be orientedEast-West at a length 9406 of the maximum East-West bonding misalignmentMx plus a delta D, which will be explained later. The pitch of thelanding strip may be twice the minimum pitch Py of this upper layer ofthe first wafer 9302. 9403 may indicate an unused potential room for anadditional metal strip.

FIG. 94B illustrates landing strips 9412, 9413 exposed at the top of thesecond wafer 9312. FIG. 94B also shows two columns of landing strips,namely, A and B going North to South. The length of these landing stripsis 1.25 Py. The two wafers 9302 and 9312 may be bonded copper-to-copperand the landing strips of FIG. 94A and FIG. 94B may be designed so thatthe bonding misalignment does not exceed the maximum misalignment Mx inthe East-West direction and My in the North-South direction. The landingstrips 9412 and 9413 of FIG. 94B may be designed so that they may neverunintentionally short to landing strips 9402 of 94A and that either rowA landing strips 9412 or row B landing strips 9413 may achieve fullcontact with landing strips 9402. The delta D may be the size from theEast edge of landing strips 9413 of row B to the West edge of A landingstrips 9412. The number of landing strips 9412 and 9413 of FIG. 94B maybe designed to cover the FIG. 94A landing strips 9402 plus My to covermaximum misalignment error in the North-South direction.

Substantially all the landing strips 9412 and 9413 of FIG. 94B may berouted by the internal routing of the top wafer 9312 to the bottom ofthe wafer next to the transistor layers. The location on the bottom ofthe wafer is illustrated in FIG. 93D as the upper side of the 9322structure. Now new vias 9432 may be formed to connect the landing stripsto the top surface of the bonded structure using conventional waferprocessing steps. FIG. 94C illustrates all the via connections routed tothe landing strips of FIG. 94B, arranged in row A 9432 and row B 9433.In addition, the vias 9436 for bringing in the signals may also beprocessed. All these vias may be aligned to the top wafer 9312.

As illustrated in FIG. 94C, a metal mask may now be used to connect, forexample, four of the vias 9432 and 9433 to the four vias 9436 usingmetal strips 9438. This metal mask may be aligned to the top wafer 9312in the East-West direction. This metal mask may also be aligned to thetop wafer 9312 in the North-South direction but with a special offsetthat is based on the bonding misalignment in the North-South direction.The length of the metal structure 9438 in the North South direction maybe enough to cover the worst case North-South direction bondingmisalignment.

It should be stated again that the present invention could be applied tomany applications other than programmable logic such a GraphicsProcessor which may comprise many repeating processing units. Otherapplications might include general logic design in 3D ASICs (ApplicationSpecific Integrated Circuits) or systems combining ASIC layers withlayers comprising at least in part other special functions. Persons ofordinary skill in the art will appreciate that many more embodiment andcombinations are possible by employing the inventive principlescontained herein and such embodiments will readily suggest themselves tosuch skilled persons. Thus the invention is not to be limited in any wayexcept by the appended claims.

Yet another alternative to implement 3D redundancy to improve yield byreplacing a defective circuit is by the use of Direct Write E-beaminstead of a programmable connection.

An additional variation of the programmable 3D system may comprise atiled array of programmable logic tiles connected with I/O structuresthat are pre fabricated on the base wafer 1402 of FIG. 14.

In yet an additional variation, the programmable 3D system may comprisea tiled array of programmable logic tiles connected with I/O structuresthat are pre-fabricated on top of the finished base wafer 1402 by usingany of the techniques presented in conjunction to FIGS. 21-35 or FIGS.39-40. In fact any of the alternative structures presented in FIG. 11may be fabricated on top of each other by the 3D techniques presented inconjunction with FIGS. 21-35 or FIGS. 39-40. Accordingly many variationsof 3D programmable systems may be constructed with a limited set ofmasks by mixing different structures to form various 3D programmablesystems by varying the amount and 3D position of logic and type of I/Osand type of memories and so forth.

Additional flexibility and reuse of masks may be achieved by utilizingonly a portion of the full reticle exposure. Modern steppers allowcovering portions of the reticle and hence projecting only a portion ofthe reticle. Accordingly a portion of a mask set may be used for onefunction while another portion of that same mask set would be used foranother function. For example, let the structure of FIG. 37 representthe logic portion of the end device of a 3D programmable system. On topof that 3×3 programmable tile structure I/O structures could be builtutilizing process techniques according to FIGS. 21-35 or FIGS. 39-40.There may be a set of masks where various portions provide for theoverlay of different I/O structures; for example, one portion comprisingsimple I/Os, and another of Serializer/Deserializer (Ser/Des) I/Os. Eachset is designed to provide tiles of I/O that perfectly overlay theprogrammable logic tiles. Then out of these two portions on one maskset, multiple variations of end systems could be produced, including onewith all nine tiles as simple I/Os, another with SerDes overlaying tile(0,0) while simple I/Os are overlaying the other eight tiles, anotherwith SerDes overlaying tiles (0,0), (0,1) and (0,2) while simple I/Osare overlaying the other 6 tiles, and so forth. In fact, if properlydesigned, multiples of layers could be fabricated one on top of theother offering a large variety of end products from a limited set ofmasks. Persons of ordinary skill in the art will appreciate that thistechnique has applicability beyond programmable logic and may profitablybe employed in the construction of many 3D ICs and 3D systems. Thus thescope of the invention is only to be limited by the appended claims.

In yet an additional alternative of the present invention, the 3Dantifuse Configurable System, may also comprise a Programming Die. Insome cases of FPGA products, and primarily in antifuse-based products,there is an external apparatus that may be used for the programming thedevice. In many cases it is a user convenience to integrate thisprogramming function into the FPGA device. This may result in asignificant die overhead as the programming process needs highervoltages as well as control logic. The programmer function could bedesigned into a dedicated Programming Die. Such a Programmer Die couldcomprise the charge pump, to generate the higher programming voltage,and a controller with the associated programming to program the antifuseconfigurable dies within the 3D Configurable circuits, and theprogramming check circuits. The Programming Die might be fabricatedusing a lower cost older semiconductor process. An additional advantageof this 3D architecture of the Configurable System may be a high volumecost reduction option wherein the antifuse layer may be replaced with acustom layer and, therefore, the Programming Die could be removed fromthe 3D system for a more cost effective high volume production.

It will be appreciated by persons of ordinary skill in the art, that thepresent invention is using the term antifuse as it is the common name inthe industry, but it also refers in this present invention to any microelement that functions like a switch, meaning a micro element thatinitially has highly resistive-OFF state, and electronically it could bemade to switch to a very low resistance-ON state. It could alsocorrespond to a device to switch ON-OFF multiple times—a re-programmableswitch. As an example there are new innovations, such as theelectro-statically actuated Metal-Droplet micro-switch introduced by C.J. Kim of UCLA micro & nano manufacturing lab, that may be compatiblefor integration onto CMOS chips.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to antifuse configurable logic and it will beapplicable to other non-volatile configurable logic. A good example forsuch is the Flash based configurable logic. Flash programming may alsoneed higher voltages, and having the programming transistors and theprogramming circuits in the base diffusion layer may reduce the overalldensity of the base diffusion layer. Using various embodiments of thepresent invention may be useful and could allow a higher device density.It is therefore suggested to build the programming transistors and theprogramming circuits, not as part of the diffusion layer, but accordingto one or more embodiments of the present invention. In high volumeproduction one or more custom masks could be used to replace thefunction of the Flash programming and accordingly save the need to addon the programming transistors and the programming circuits.

Unlike metal-to-metal antifuses that could be placed as part of themetal interconnection, Flash circuits need to be fabricated in the basediffusion layers. As such it might be less efficient to have theprogramming transistor in a layer far above. An alternative embodimentof the present invention is to use Through-Silicon-Via 816 to connectthe configurable logic device and its Flash devices to an underlyingstructure 814 comprising the programming transistors.

In this document, various terms have been used while generally referringto the element. For example, “house” refers to the firstmono-crystalline layer with its transistors and metal interconnectionlayer or layers. This first mono-crystalline layer has also beenreferred to as the main wafer and sometimes as the acceptor wafer andsometimes as the base wafer.

Some embodiments of the present invention may include alternativetechniques to build IC (Integrated Circuit) devices including techniquesand methods to construct 3D IC systems. Some embodiments of the presentinvention may enable device solutions with far less power consumptionthan prior art. These device solutions could be very useful for thegrowing application of mobile electronic devices and mobile systems suchas mobile phones, smart phone, cameras and the like. For example,incorporating the 3D IC semiconductor devices according to someembodiments of the present invention within these mobile electronicdevices and mobile systems could provide superior mobile units thatcould operate much more efficiently and for a much longer time than withprior art technology.

3D ICs according to some embodiments of the present invention could alsoenable electronic and semiconductor devices with much a higherperformance due to the shorter interconnect as well as semiconductordevices with far more complexity via multiple levels of logic andproviding the ability to repair or use redundancy. The achievablecomplexity of the semiconductor devices according to some embodiments ofthe present invention could far exceed what was practical with the priorart technology. These advantages could lead to more powerful computersystems and improved systems that have embedded computers.

Some embodiments of the present invention may also enable the design ofstate of the art electronic systems at a greatly reduced non-recurringengineering (NRE) cost by the use of high density 3D FPGAs or variousforms of 3D array base ICs with reduced custom masks as been describedpreviously. These systems could be deployed in many products and in manymarket segments. Reduction of the NRE may enable new product family orapplication development and deployment early in the product lifecycle bylowering the risk of upfront investment prior to a market beingdeveloped. The above advantages may also be provided by various mixessuch as reduced NRE using generic masks for layers of logic and othergeneric mask for layers of memories and building a very complex systemusing the repair technology to overcome the inherent yield limitation.Another form of mix could be building a 3D FPGA and add on it 3D layersof customizable logic and memory so the end system could have fieldprogrammable logic on top of the factory customized logic. In fact thereare many ways to mix the many innovative elements to form 3D IC tosupport the need of an end system, including using multiple deviceswherein more than one device incorporates elements of the presentinvention. An end system could benefits from memory device utilizing theinvention 3D memory together with high performance 3D FPGA together withhigh density 3D logic and so forth. Using devices that use one ormultiple elements of the present invention would allow for betterperformance and or lower power and other advantages resulting from thepresent inventions to provide the end system with a competitive edge.Such end system could be electronic based products or other type ofsystems that include some level of embedded electronics, such as, forexample, cars, remote controlled vehicles, etc.

To improve the contact resistance of very small scaled contacts, thesemiconductor industry employs various metal silicides, such as, forexample, cobalt silicide, titanium silicide, tantalum silicide, andnickel silicide. The current advanced CMOS processes, such as, forexample, 45 nm, 32 nm, and 22 nm employ nickel silicides to improve deepsubmicron source and drain contact resistances. Background informationon silicides utilized for contact resistance reduction can be found in“NiSi Salicide Technology for Scaled CMOS,” H. Iwai, et. al.,Microelectronic Engineering, 60 (2002), pp 157-169; “Nickel vs. CobaltSilicide integration for sub-50 nm CMOS”, B. Froment, et. al., IMEC ESSCircuits, 2003; and “65 and 45-nm Devices—an Overview”, D. James,Semicon West, July 2008, ctr_(—)024377. To achieve the lowest nickelsilicide contact and source/drain resistances, the nickel on silicon canbe heated to approximately 450° C.

Thus it may be desirable to enable low resistances for process flows inthis document where the post layer transfer temperature exposures mustremain under approximately 400° C. due to metallization, such as, forexample, copper and aluminum, and low-k dielectrics present.

For junction-less transistors (JLTs), in particular, forming contacts isa serious challenge. This is because the doping of JLTs should be keptlow (below approximately 0.5-5×10¹⁹/cm³ or so) to enable good transistoroperation but should be kept high (above approximately 0.5-5×10¹⁹/cm³ orso) to enable low contact resistance. A technique to obtain low contactresistance at lower doping values is therefore desirable. One suchembodiment of the present invention is by utilizing silicides withdifferent work-functions for n type JLTs than for p type JLTs inventiontechnique to obtain low resistance at lower doping values. For example,high work function materials, including, such materials as, Palladiumsilicide, may be used to make contact to p-type JLTs and lowerwork-function materials, including, such as, Erbium silicide, may beused to make contact to n-type JLTs. These types of approaches are notgenerally used in the manufacturing of planar inversion-mode MOSFETs.This is due to separate process steps and increased cost for formingseparate contacts to n type and p type transistors on the same devicelayer. However, for 3D integrated approaches where p-type JLTs arestacked above n-type JLTs and vice versa, it is not costly to formsilicides with uniquely optimized work functions for n type and p typetransistors. Furthermore, for JLTs where contact resistance may be anissue, the additional cost of using separate silicides for n type and ptype transistors on the same device layer may be acceptable.

The example process flow shown below forms a Recessed Channel ArrayTransistor (RCAT) with low contact resistance, but this or similar flowsmay be applied to other process flows and devices, such as, for example,S-RCAT, JLT, V-groove, JFET, bipolar, and replacement gate flows.

A planar n-channel Recessed Channel Array Transistor (RCAT) with metalsilicide source & drain contacts suitable for a 3D IC may beconstructed. As illustrated in FIG. 133A, a P− substrate donor wafer13302 may be processed to include wafer sized layers of N+ doping 13304,and P− doping 13301 across the wafer. The N+ doped layer 13304 may beformed by ion implantation and thermal anneal. In addition, P− dopedlayer 13301 may have additional ion implantation and anneal processingto provide a different dopant level than P− substrate 13302. P− dopedlayer 13301 may also have graded P− doping to mitigate transistorperformance issues, such as, for example, short channel effects, afterthe RCAT is formed. The layer stack may alternatively be formed bysuccessive epitaxially deposited doped silicon layers of P− doping 13301and N+ doping 13304, or by a combination of epitaxy and implantation.Annealing of implants and doping may utilize optical annealingtechniques or types of Rapid Thermal Anneal (RTA or spike).

As illustrated in FIG. 133B, a silicon reactive metal, such as, forexample, Nickel or Cobalt, may be deposited onto N+ doped layer 13304and annealed, utilizing anneal techniques such as, for example, RTA,thermal, or optical, thus forming metal silicide layer 13306. The topsurface of donor wafer 13301 may be prepared for oxide wafer bondingwith a deposition of an oxide to form oxide layer 13308.

As illustrated in FIG. 133C, a layer transfer demarcation plane (shownas dashed line) 13399 may be formed by hydrogen implantation or othermethods as previously described.

As illustrated in FIG. 133D donor wafer 13302 with layer transferdemarcation plane 13399, P− doped layer 13301, N+ doped layer 13304,metal silicide layer 13306, and oxide layer 13308 may be temporarilybonded to carrier or holder substrate 13312 with a low temperatureprocess that may facilitate a low temperature release. The carrier orholder substrate 13312 may be a glass substrate to enable state of theart optical alignment with the acceptor wafer. A temporary bond betweenthe carrier or holder substrate 13312 and the donor wafer 13302 may bemade with a polymeric material, such as, for example, polyimide DuPontHD3007, which can be released at a later step by laser ablation,Ultra-Violet radiation exposure, or thermal decomposition, shown asadhesive layer 13314. Alternatively, a temporary bond may be made withuni-polar or bi-polar electrostatic technology such as, for example, theApache tool from Beam Services Inc.

As illustrated in FIG. 133E, the portion of the donor wafer 13302 thatis below the layer transfer demarcation plane 13399 may be removed bycleaving or other processes as previously described, such as, forexample, ion-cut or other methods. The remaining donor wafer P− dopedlayer 13301 may be thinned by chemical mechanical polishing (CMP) sothat the P− layer 13316 may be formed to the desired thickness. Oxide13318 may be deposited on the exposed surface of P− layer 13316.

As illustrated in FIG. 133F, both the donor wafer 13302 and acceptorsubstrate or wafer 13310 may be prepared for wafer bonding as previouslydescribed and then low temperature (less than approximately 400° C.)aligned and oxide to oxide bonded. Acceptor substrate 13310, asdescribed previously, may include, for example, transistors, circuitry,metal, such as, for example, aluminum or copper, interconnect wiring,and thru layer via metal interconnect strips or pads. The carrier orholder substrate 13312 may then be released using a low temperatureprocess such as, for example, laser ablation. Oxide layer 13318, P−layer 13316, N+ doped layer 13304, metal silicide layer 13306, and oxidelayer 13308 have been layer transferred to acceptor wafer 13310. The topsurface of oxide 13308 may be chemically or mechanically polished. NowRCAT transistors are formed with low temperature (less thanapproximately 400° C.) processing and aligned to the acceptor wafer13310 alignment marks (not shown).

As illustrated in FIG. 133G, the transistor isolation regions 13322 maybe formed by mask defining and then plasma/RIE etching oxide layer13308, metal silicide layer 13306, N+ doped layer 13304, and P− layer13316 to the top of oxide layer 13318. Then a low-temperature gap filloxide may be deposited and chemically mechanically polished, with theoxide remaining in isolation regions 13322. Then the recessed channel13323 may be mask defined and etched. The recessed channel surfaces andedges may be smoothed by wet chemical or plasma/RIE etching techniquesto mitigate high field effects. These process steps form oxide regions13324, metal silicide source and drain regions 13326, N+ source anddrain regions 13328 and P− channel region 13330.

As illustrated in FIG. 133H, a gate dielectric 13332 may be formed and agate metal material may be deposited. The gate dielectric 13332 may bean atomic layer deposited (ALD) gate dielectric that is paired with awork function specific gate metal in the industry standard high k metalgate process schemes described previously. Or the gate dielectric 13332may be formed with a low temperature oxide deposition or low temperaturemicrowave plasma oxidation of the silicon surfaces and then a gatematerial such as, for example, tungsten or aluminum may be deposited.Then the gate material may be chemically mechanically polished, and thegate area defined by masking and etching, thus forming gate electrode13334.

As illustrated in FIG. 133I, a low temperature thick oxide 13338 isdeposited and source, gate, and drain contacts, and thru layer via (notshown) openings are masked and etched preparing the transistors to beconnected via metallization. Thus gate contact 13342 connects to gateelectrode 13334, and source & drain contacts 13336 connect to metalsilicide source and drain regions 13326.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 133A through 133I are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the temporary carriersubstrate may be replaced by a carrier wafer and a permanently bondedcarrier wafer flow such as described in FIG. 40 may be employed. Manyother modifications within the scope of the invention will suggestthemselves to such skilled persons after reading this specification.Thus the invention is to be limited only by the appended claims.

With the high density of layer to layer interconnection and theformation of memory devices & transistors that are enabled byembodiments in this document, novel FPGA (Field Programmable Gate Array)programming architectures and devices may be employed to create cost,area, and performance efficient 3D FPGAs. The pass transistor, orswitch, and the memory device that controls the ON or OFF state of thepass transistor may reside in separate layers and may be connected bythru layer vias (TLVs) to each other and the routing network metallines, or the pass transistor and memory devices may reside in the samelayer and TLVs may be utilized to connect to the network metal lines.

As illustrated in FIG. 134A, acceptor wafer 13400 may be processed tocompromise logic circuits, analog circuits, and other devices, withmetal interconnection and a metal configuration network to form the baseFPGA. Acceptor wafer 13400 may also include configuration elements suchas, for example, switches, pass transistors, memory elements,programming transistors, and may contain a foundation layer or layers asdescribed previously.

As illustrated in FIG. 134B, donor wafer 13402 may be preprocessed witha layer or layers of pass transistors or switches or partially formedpass transistors or switches. The pass transistors may be constructedutilizing the partial transistor process flows described previously,such as, for example, RCAT or JLT or others, or may utilize thereplacement gate techniques, such as, for example, CMOS or CMOS N over Por gate array, with or without a carrier wafer, as described previously.Donor wafer 13402 and acceptor substrate 13400 and associated surfacesmay be prepared for wafer bonding as previously described.

As illustrated in FIG. 134C, donor wafer 13402 and acceptor substrate13400 may be bonded at a low temperature (less than approximately 400°C.) and a portion of donor wafer 13402 may be removed by cleaving andpolishing, or other processes as previously described, such as, forexample, ion-cut or other methods, thus forming the remaining passtransistor layer 13402′. Now transistors or portions of transistors maybe formed or completed and may be aligned to the acceptor substrate13400 alignment marks (not shown) as described previously. Thru layervias (TLVs) 13410 may be formed as described previously and as well asinterconnect and dielectric layers. Thus acceptor substrate with passtransistors 13400A is formed, which may include acceptor substrate13400, pass transistor layer 13402′, and TLVs 13410.

As illustrated in FIG. 134D, memory element donor wafer 13404 may bepreprocessed with a layer or layers of memory elements or partiallyformed memory elements. The memory elements may be constructed utilizingthe partial memory process flows described previously, such as, forexample, RCAT DRAM, JLT, or others, or may utilize the replacement gatetechniques, such as, for example, CMOS gate array to form SRAM elements,with or without a carrier wafer, as described previously, or may beconstructed with non-volatile memory, such as, for example, R-RAM or FGFlash as described previously. Memory element donor wafer 13404 andacceptor substrate 13400A and associated surfaces may be prepared forwafer bonding as previously described.

As illustrated in FIG. 134E, memory element donor wafer 13404 andacceptor substrate 13400A may be bonded at a low temperature (less thanapproximately 400° C.) and a portion of memory element donor wafer 13404may be removed by cleaving and polishing, or other processes aspreviously described, such as, for example, ion-cut or other methods,thus forming the remaining memory element layer 13404′. Now memoryelements & transistors or portions of memory elements & transistors maybe formed or completed and may be aligned to the acceptor substrate13400A alignment marks (not shown) as described previously. Memory toswitch thru layer vias 13420 and memory to acceptor thru layer vias13430 as well as interconnect and dielectric layers may be formed asdescribed previously. Thus acceptor substrate with pass transistors andmemory elements 13400B is formed, which may include acceptor substrate13400, pass transistor layer 13402′, TLVs 13410, memory to switch thrulayer vias 13420, memory to acceptor thru layer vias 13430, and memoryelement layer 13404′.

As illustrated in FIG. 134F, a simple schematic of important elements ofacceptor substrate with pass transistors and memory elements 13400B isshown. An exemplary memory element 13440 residing in memory elementlayer 13404′ may be electrically coupled to exemplary pass transistorgate 13442, residing in pass transistor layer 13402′, with memory toswitch thru layer vias 13420. The pass transistor source 13444, residingin pass transistor layer 13402′, may be electrically coupled to FPGAconfiguration network metal line 13446, residing in acceptor substrate13400, with TLV 13410A. The pass transistor drain 13445, residing inpass transistor layer 13402′, may be electrically coupled to FPGAconfiguration network metal line 13447, residing in acceptor substrate13400, with TLV 13410B. The memory element 13440 may be programmed withsignals from off chip, or above, within, or below the memory elementlayer 13404′. The memory element 13440 may also include an inverterconfiguration, wherein one memory cell, such as, for example, a FG Flashcell, may couple the gate of the pass transistor to power supply Vcc ifturned on, and another FG Flash device may couple the gate of the passtransistor to ground if turned on. Thus, FPGA configuration networkmetal line 13446, which may be carrying the output signal from a logicelement in acceptor substrate 13400, may be electrically coupled to FPGAconfiguration network metal line 13447, which may route to the input ofa logic element elsewhere in acceptor substrate 13430.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 134A through 134F are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the memory element layer13404′ may be constructed below pass transistor layer 13402′.Additionally, the pass transistor layer 13402′ may include control andlogic circuitry in addition to the pass transistors or switches.Moreover, the memory element layer 13404′ may comprise control and logiccircuitry in addition to the memory elements. Further, that the passtransistor element may instead be a transmission gate, or may be anactive drive type switch. Many other modifications within the scope ofthe invention will suggest themselves to such skilled persons afterreading this specification. Thus the invention is to be limited only bythe appended claims.

The pass transistor, or switch, and the memory device that controls theON or OFF state of the pass transistor may reside in the same layer andTLVs may be utilized to connect to the network metal lines. Asillustrated in FIG. 135A, acceptor wafer 13500 may be processed tocompromise logic circuits, analog circuits, and other devices, withmetal interconnection and a metal configuration network to form the baseFPGA. Acceptor wafer 13500 may also include configuration elements suchas, for example, switches, pass transistors, memory elements,programming transistors, and may contain a foundation layer or layers asdescribed previously.

As illustrated in FIG. 135B, donor wafer 13502 may be preprocessed witha layer or layers of pass transistors or switches or partially formedpass transistors or switches. The pass transistors may be constructedutilizing the partial transistor process flows described previously,such as, for example, RCAT or JLT or others, or may utilize thereplacement gate techniques, such as, for example, CMOS or CMOS N over Por CMOS gate array, with or without a carrier wafer, as describedpreviously. Donor wafer 13502 may be preprocessed with a layer or layersof memory elements or partially formed memory elements. The memoryelements may be constructed utilizing the partial memory process flowsdescribed previously, such as, for example, RCAT DRAM or others, or mayutilize the replacement gate techniques, such as, for example, CMOS gatearray to form SRAM elements, with or without a carrier wafer, asdescribed previously. The memory elements may be formed simultaneouslywith the pass transistor, for example, such as, for example, byutilizing a CMOS gate array replacement gate process where a CMOS passtransistor and SRAM memory element, such as a 6-transistor cell, may beformed, or an RCAT pass transistor formed with an RCAT DRAM memory.Donor wafer 13502 and acceptor substrate 13500 and associated surfacesmay be prepared for wafer bonding as previously described.

As illustrated in FIG. 135C, donor wafer 13502 and acceptor substrate13500 may be bonded at a low temperature (less than approximately 400°C.) and a portion of donor wafer 13502 may be removed by cleaving andpolishing, or other processes as previously described, such as, forexample, ion-cut or other methods, thus forming the remaining passtransistor & memory layer 13502′. Now transistors or portions oftransistors and memory elements may be formed or completed and may bealigned to the acceptor substrate 13500 alignment marks (not shown) asdescribed previously. Thru layer vias (TLVs) 13510 may be formed asdescribed previously. Thus acceptor substrate with pass transistors &memory elements 13500A is formed, which may include acceptor substrate13500, pass transistor & memory element layer 13502′, and TLVs 13510.

As illustrated in FIG. 135D, a simple schematic of important elements ofacceptor substrate with pass transistors & memory elements 13500A isshown. An exemplary memory element 13540 residing in pass transistor &memory layer 13502′ may be electrically coupled to exemplary passtransistor gate 13542, also residing in pass transistor & memory layer13502′, with pass transistor & memory layer interconnect metallization13525. The pass transistor source 13544, residing in pass transistor &memory layer 13502′, may be electrically coupled to FPGA configurationnetwork metal line 13546, residing in acceptor substrate 13500, with TLV13510A. The pass transistor drain 13545, residing in pass transistor &memory layer 13502′, may be electrically coupled to FPGA configurationnetwork metal line 13547, residing in acceptor substrate 13500, with TLV13510B. The memory element 13540 may be programmed with signals from offchip, or above, within, or below the pass transistor & memory layer13502′. The memory element 13540 may also include an inverterconfiguration, wherein one memory cell, such as, for example, a FG Flashcell, may couple the gate of the pass transistor to power supply Vcc ifturned on, and another FG Flash device may couple the gate of the passtransistor to ground if turned on. Thus, FPGA configuration networkmetal line 13546, which may be carrying the output signal from a logicelement in acceptor substrate 13500, may be electrically coupled to FPGAconfiguration network metal line 13547, which may route to the input ofa logic element elsewhere in acceptor substrate 13530.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 135A through 135D are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the pass transistor &memory layer 13502′ may include control and logic circuitry in additionto the pass transistors or switches and memory elements. Additionally,that the pass transistor element may instead be a transmission gate, ormay be an active drive type switch. Many other modifications within thescope of the invention will suggest themselves to such skilled personsafter reading this specification. Thus the invention is to be limitedonly by the appended claims.

As illustrated in FIG. 136, a non-volatile configuration switch withintegrated floating gate (FG) Flash memory is shown. The control gate13602 and floating gate 13604 are common to both the sense transistorchannel 13620 and the switch transistor channel 13610. Switch transistorsource 13612 and switch transistor drain 13614 may be coupled to theFPGA configuration network metal lines. The sense transistor source13622 and the sense transistor drain 13624 may be coupled to theprogram, erase, and read circuits. This integrated NVM switch has beenutilized by FPGA maker Actel Corporation and is manufactured in a hightemperature (greater than approximately 400° C.) 2D embedded FG flashprocess technology.

As illustrated in FIGS. 137A to 137G, a 1T NVM FPGA cell may beconstructed with a single layer transfer of wafer sized doped layers andpost layer transfer processing with a process flow that is suitable for3D IC manufacturing. This cell may be programmed with signals from offchip, or above, within, or below the cell layer.

As illustrated in FIG. 137A, a P− substrate donor wafer 13700 may beprocessed to include two wafer sized layers of N+ doping 13704 and P−doping 13706. The P− doped layer 13706 may have the same or a differentdopant concentration than the P-substrate 13700. The doped layers may beformed by ion implantation and thermal anneal. The layer stack mayalternatively be formed by successive epitaxially deposited dopedsilicon layers or by a combination of epitaxy and implantation andanneals. P− doped layer 13706 and N+ doped layer 13704 may also havegraded doping to mitigate transistor performance issues, such as, forexample, short channel effects, and enhance programming and eraseefficiency. A screen oxide 13701 may be grown or deposited before animplant to protect the silicon from implant contamination and to providean oxide surface for later wafer to wafer bonding. These processes maybe done at temperatures above 400° C. as the layer transfer to theprocessed substrate with metal interconnects has yet to be done.

As illustrated in FIG. 137B, the top surface of donor wafer 13700 may beprepared for oxide wafer bonding with a deposition of an oxide 13702 orby thermal oxidation of the P− doped layer 13706 to form oxide layer13702, or a re-oxidation of implant screen oxide 13701. A layer transferdemarcation plane 13799 (shown as a dashed line) may be formed in donorwafer 13700 (shown) or N+ doped layer 13704 by hydrogen implantation13707 or other methods as previously described. Both the donor wafer13700 and acceptor wafer 13710 may be prepared for wafer bonding aspreviously described and then low temperature (less than approximately400° C.) bonded. The portion of the P− donor wafer substrate 13700 thatis above the layer transfer demarcation plane 13799 may be removed bycleaving and polishing, or other low temperature processes as previouslydescribed. This process of an ion implanted atomic species, such as, forexample, Hydrogen, forming a layer transfer demarcation plane, andsubsequent cleaving or thinning, may be called ‘ion-cut’. Acceptor wafer13710 may have similar meanings as wafer 808 previously described withreference to FIG. 8.

As illustrated in FIG. 137C, the remaining N+ doped layer 13704′ and P−doped layer 13706, and oxide layer 13702 have been layer transferred toacceptor wafer 13710. The top surface of N+ doped layer 13704′ may bechemically or mechanically polished smooth and flat. Now FG and othertransistors may be formed with low temperature (less than approximately400° C.) processing and aligned to the acceptor wafer 13710 alignmentmarks (not shown). For illustration clarity, the oxide layers, such as,for example, 13702, used to facilitate the wafer to wafer bond are notshown in subsequent drawings.

As illustrated in FIG. 137D, the transistor isolation regions may belithographically defined and then formed by plasma/RIE etch removal ofportions of N+ doped layer 13704′ and P− doped layer 13706 to at leastthe top oxide of acceptor substrate 13710. Then a low-temperature gapfill oxide may be deposited and chemically mechanically polished,remaining in transistor isolation regions 13720 and SW-to-SE isolationregion 13721. “SW’ in the FIG. 137 illustrations denotes that portion ofthe illustration where the switch transistor will be formed, and ‘SE’denotes that portion of the illustration where the sense transistor willbe formed. Thus formed are future SW transistor regions N+ doped 13714and P− doped 13716, and future SE transistor regions N+ doped 13715, andP− doped 13717.

As illustrated in FIG. 137E, the SW recessed channel 13742 and SErecessed channel 13743 may be lithographically defined and etched,removing portions future SW transistor regions N+ doped 13714 and P−doped 13716, and future SE transistor regions N+ doped 13715, and P−doped 13717. The recessed channel surfaces and edges may be smoothed bywet chemical or plasma/RIE etching techniques to mitigate high fieldeffects. The SW recessed channel 13742 and SE recessed channel 13743 maybe mask defined and etched separately or at the same step. The SWchannel width may be larger than the SE channel width. These processsteps form SW source and drain regions 13724, SE source and drainregions 13725, SW transistor channel region 13716 and SE transistorchannel region 13717.

As illustrated in FIG. 137F, a tunneling dielectric 13711 may be formedand a floating gate material may be deposited. The tunneling dielectric13711 may be an atomic layer deposited (ALD) dielectric. Or thetunneling dielectric 13711 may be formed with a low temperature oxidedeposition or low temperature microwave plasma oxidation of the siliconsurfaces. Then a floating gate material, such as, for example, dopedpoly-crystalline or amorphous silicon, may be deposited. Then thefloating gate material may be chemically mechanically polished, and thefloating gate 13752 may be partially or fully formed by lithographicdefinition and plasma/RIE etching.

As illustrated in FIG. 137G, an inter-poly dielectric 13741 may beformed by either low temperature oxidation and depositions of adielectric or layers of dielectrics, such as, for example,oxide-nitride-oxide (ONO) layers, and then a control gate material, suchas, for example, doped poly-crystalline or amorphous silicon, may bedeposited. The control gate material may be chemically mechanicallypolished, and the control gate 13754 may be formed by lithographicdefinition and plasma/RIE etching. The etching of control gate 13754 mayalso include etching portions of the inter-poly dielectric and portionsof the floating gate 13752 in a self-aligned stack etch process. Logictransistors for control functions may be formed (not shown) utilizing 3DIC compatible methods described in the document, such as, for example,RCAT, V-groove, and contacts, including thru layer vias, andinterconnect metallization may be constructed. This flow enables theformation of a mono-crystalline silicon 1T NVM FPGA configuration cellconstructed in a single layer transfer of prefabricated wafer sizeddoped layers, which may be formed and connected to the underlyingmulti-metal layer semiconductor device without exposing the underlyingdevices to a high temperature.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 137A through 137G are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the floating gate mayinclude nano-crystals of silicon or other materials. Additionally, thata common well cell may be constructed by removing the SW-to-SE isolation13721. Moreover, that the slope of the recess of the channel transistormay be from zero to 180 degrees. Further, that logic transistors anddevices may be constructed by using the control gate as the device gate.Additionally, that the logic device gate may be made separately from thecontrol gate formation. Moreover, the 1T NVM FPGA configuration cell maybe constructed with a charge trap technique NVM, a resistive memorytechnique, and may also have a junction-less SW or SE transistorconstruction. Many other modifications within the scope of the inventionwill suggest themselves to such skilled persons after reading thisspecification. Thus the invention is to be limited only by the appendedclaims.

It will also be appreciated by persons of ordinary skill in the art thatthe present invention is not limited to what has been particularly shownand described hereinabove. For example, drawings or illustrations maynot show n or p wells for clarity. Rather, the scope of the presentinvention includes both combinations and sub-combinations of the variousfeatures described hereinabove as well as modifications and variationswhich would occur to such skilled persons upon reading the foregoingdescription. Thus the invention is to be limited only by the appendedclaims.

1. A semiconductor device comprising: a first layer comprising aplurality of first transistors, wherein said plurality of firsttransistors construct a plurality of first logic circuits, and whereinsaid plurality of first logic circuits comprise a plurality offlip-flops; and a second layer overlaying said first layer, said secondlayer comprising a plurality of second transistors, wherein said secondtransistors are mono-crystal transistors; wherein said plurality ofsecond transistors construct a plurality of second logic circuits;wherein each logic circuit in said plurality of first logic circuits hasat least one first output, wherein each logic circuit in said pluralityof second logic circuits has a second output, and wherein said pluralityof first transistors comprise a plurality of first selectors adapted toselectively replace at least one of said first outputs with at least oneof said second outputs.
 2. A semiconductor device according to claim 1,wherein said second layer has a thickness less than 1 micron.
 3. Asemiconductor device according to claim 1, wherein each logic circuit insaid plurality of first logic circuits has at least one input coupled toan input to one of said second logic circuits.
 4. A semiconductor deviceaccording to claim 1, further comprising: a plurality of circuitsadapted to perform a comparison between one of said first outputs andone of said second outputs.
 5. A semiconductor device according to claim1, wherein said at least one first output is either an output of aflip-flop or an input of a flip-flop.
 6. A semiconductor deviceaccording to claim 1, further comprising: a controller adapted toperform testing of said semiconductor device.
 7. A semiconductor devicecomprising: a first layer comprising a plurality of first transistors,wherein said plurality of first transistors construct a plurality offirst logic circuits, and wherein said plurality of first logic circuitscomprise a plurality of flip-flops; and a second layer overlaying saidfirst layer, said second layer comprising a plurality of secondtransistors, wherein said second transistors are mono-crystaltransistors; wherein said plurality of second transistors construct aplurality of second logic circuits; wherein at least one of saidplurality of first logic circuits includes a selector adapted to replacesaid at least one of said plurality of first logic circuits with one ofsaid plurality of second logic circuits to repair operation of saidsemiconductor device.
 8. A semiconductor device according to claim 7,wherein said second layer has a thickness less than 1 micron.
 9. Asemiconductor device according to claim 7, wherein said first layercomprises a plurality of flip-flops and each flip-flop in said pluralityof flip-flops has an input and an output, wherein either said input oroutput is selectively coupleable to said second layer.
 10. Asemiconductor device according to claim 7, further comprising: aplurality of circuits each adapted to perform a comparison between asignal generated by said first layer and a signal generated by saidsecond layer.
 11. A semiconductor device according to claim 7, whereinsaid first layer comprises a plurality of flip-flops and each flip-flopin said plurality of flip-flops has a selectively coupleable additionalinput generated by said second transistor.
 12. A semiconductor deviceaccording to claim 7, further comprising: a controller adapted toperform testing of said semiconductor device.
 13. A semiconductor devicecomprising: a first layer comprising a plurality of first transistorsconstructing logic circuits; and a second layer comprising a pluralityof second transistors, wherein said second transistors are mono-crystaltransistors; wherein said plurality of second transistors overlays saidplurality of first transistors and construct redundancy circuits forsaid logic circuits of said plurality of first transistors; and whereinsaid first layer comprises a plurality of flip-flops and each flip-flopin said plurality of flip-flops has an input and an output, whereineither said input or said output is selectively coupleable to saidsecond layer.
 14. A semiconductor device according to claim 13, whereinfabrication of said device comprises layer transfer.
 15. A semiconductordevice according to claim 13, further comprising: a plurality ofcircuits each adapted to perform a comparison between a signal generatedby said first layer and a signal generated by said second layer.
 16. Asemiconductor device according to claim 13, wherein said first layercomprises a plurality of flip-flops and each flip-flop in said pluralityof flip-flops has a selectively coupleable additional input generated bysaid second transistor.
 17. A semiconductor device according to claim13, further comprising: a controller adapted to perform testing of saidsemiconductor device.